Heat Exchangers & Overheating

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Sailnet Tayana List

I found a couple of sources for heat exchangers. One name I got from Harvey, Harpur Marine in Wilmington, CA at 310-830-0693. The other is in PA - http://www.i-netmarine.com/ . I was looking for the exchanger that mounts horizontally on the rear of the Perkins 4-108. Both places have it, both OEM (expensive) and after market from Seakamp, part # NA 001406.

Ray Slaninka November 2000

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I only bought the Heat Exchanger from Harpur Marine, not a complete engine. But you could contact them. The person I dealt with was Fred Sweers, but anybody there will be helpful. The phone number at Harpur Marine is 310-830-0693. But from where you are, it will be one hell of a long distance call. They are in Wilmington, California, (a suburb of Los Angeles). So to save you the toll call, I just phoned them. They referred me to Don Peters at S&W Diesel at phone: 310-835-3155 They specialize in Perkins. He said that he could put together a list of the components that you would need to marinized a 4-108. It would cost between $1,500 - $2,000 (salt water pump, header tank, exhaust manifold, heat exchanger, water lift exhaust e.g. Vetus, and a few other parts.). If you think you want a more detailed listing, he said he would be glad to assemble the list for you, and could ship it to you. He loves Perkins engines, and thinks that they can run forever with just a little bit of love and oil changes and fresh filters on a regular schedule. The Perkins 4-108 generates a max HP of about 47-50 HP, though at typical operating ranges, with the alternator running full output, you can expect about 35-38 HP. Ideal operating RPM is 1800-2400. Ideal temp is about 79 degrees Cent. or ca. 175 degrees Fahrenheit.

Another option that many people have exercised is to put in a Yanmar. If so, you are better off with the 45 or 50 HP not the smaller 33 HP - although many people seem quite happy with the 33 HP.

Whatever you do, according to everyone I spoke with, DO NOT use Foley Marine on the East Coast. They have a terrible reputation.

regards, Harvey November 2000

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Harvey, all

I am considering changing the MD3B Volvo to a Perkins 4108 (Sorry John but the blue smoke is causing a small smog problem over the marina). There seems to be a few on the market which have not been marinised which I am considering. Harvey could you give me your contact for Harpur, and if you have it the price you paid.

Also if anyone has details of where a complete marine kit can be purchased for a 4-108.

Bill Moloney April 2001

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The typical heat exchange that is applied to a Universal Atomic-4 @ 3 gpm rate + 35 hp ... so the BTU exchange rate should be similar ... albiet just a tad undersized) goes commercially for about $350.00 @ distributor list $. I'd be pretty sure that the manufacturer could furnish one that's 40% longer for a few extra $$$ for the extra length tubes ... as the weighted cost of manufacture is the rolling of the tubes into the tubesheet. The mounting could be on a wall of the engine compartment so you'd need to do some plumbing/hose changes, plus a few extra inserts for pencil zincs and bonding connections ..... Would save a bunch of $$$$$. You might want to alternatively check out your local "shell and tube heat exchanger" supplier or distributor for other economical alternatives. Ask/consider a U-tube bundle exchanger ... usually 2/3 the price of straight tube bundle. There's no reason for a huge cast steel headed exchanger – if you are careful with zinc anode replacement/inspection.

Rich Hampel April 2001

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I followed up a thread re 4-108 heat exchangers - you mention purchasing one made in Washington State - is the contact you gave me (swdieselinc@aol.com) a supplier for the unit you purchased ? I have been quoted US$1200 for one supplied locally.

Regards, Bill Moloney Covenant III CT37 #34 April 2001

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$1200 for the Heat Exchanger?! I assume that you really meant to write that this was the price in Kiwi dollars. I paid $350 for a brand new heat exchanger (plus shipping from L.A.). At that price I'll buy it, charge you $1,100, pocket the profit and make believe I'm doing you a favor!

Check out: http://i-netmarine.com/he/heat_exchanger-perkins4_6_cyl_models.htm

They are selling heat exchangers for the Perkins 4-107 and 4-108 for about $2500-$300(even cheaper than I paid), and I think that they are the same brand as the one I bought. Get the Cupro Nickel model. It's only about $20 more, but will last longer.

These same people sell exhaust manifolds, water lifts, etc., for very reasonable prices.

regards, Harvey April 2001

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Heat exchangers are probably BEST cleaned by using a mixture of organic acids that remove the carbonate scale but do not affect the base metal at all. Commercially available products are: Marsolve & Rydlyme - commonly used to descale heat exchangers and engine internals. So, using one of these in your system will clean the scale from the engine AND the heat exchanger AND the exhaust manifold all at the same time. You can use various inorganic acids (muriatic, etc.,) but take the risk of dissolving some of the metal. If you are experiencing rapid and repeated scale build up, especially on
the raw water side, I strongly suggest replacing the thermostat (on ANY engine) with one that opens at less then 145 degrees, as at below this temperature the carbonate salts in the sea/raw water will not precipitate out onto the metal surfaces. Its always best to operate an engine as hot as possible to enhance combustion efficiency; but, if you are constantly scaling it up, using a thermostat that opens at 145 degrees will eliminate a LOT of problems, especially on a sea/raw water cooled engine.

Rich Hampel May 2002

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Rich, we have a raw-water cooled 3QM30 with about 1,950 hours on it and it is starting to scale up. I have read about Marsolve and even found their website at http://www.marsolve.com/index.html . They recommend circulating the Marsolve for several hours through the engine. I am reluctant to spend a lot of money on their pump system and wondered if you had any ideas. One suggestion I've heard is to use a bucket and 12v bilge pump to circulate the solvent through the engine and back into the bucket but it sounds a little too Rube-Goldberg.

Gary May 2002

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A few comments about our experience with overheating: Although you are sometimes lucky and find that only one thing is causing the overheating, there are usually several contributory aspects to this. It's important to work through each of them carefully. Think of it in terms of two parallel systems: one is the salt water intake and output components, and the second is the fresh water circulation system. The heat exchanger sits between them. (The salt water system includes: raw water strainer, salt water pump, heat exchanger, exhaust system. The fresh water system is the reservoir, hoses, thermostat, and also the heat exchanger, etc.).

1) Flush out the cooling system very thoroughly. Even after many years of usage, people have noted that there is residual crud from the original casting of the engine block.

2) Replace the thermostat. Use a 158-160 degree unit. When installing, don't overdo it by putting on too much gasket sealant. It can ooze onto the thermostat and cause it to block.

3) Replace the salt water impeller in the water pump.

4) Check all hoses, and replace if they look bad

5) Make sure that there are no obstructions in the exhaust manifold

6) If in doubt, replace the heat exchanger. They contain a number of narrow and fragile copper tubes. Despite repeated cleanings by a professional shop specializing in this, the overall flow rate was inadequate. It was only after replacing it completely that we managed to bring the overheating under control.

7) CHANGE THE ZINC IN THE HEAT EXCHANGER!! Do this every time you change the oil. It is easy to overlook this. It is a major contributor to heat exchanger failures. If you have to buy one new heat exchanger, you will never again forget to replace the zincs in the future.

8) Open the intake side of the heat exchanger to remove any debris that might have gotten past your water intake strainer.

9) Check and clean the transmission cooler. It is part of the system, and is easy overlooked (I refer to the Perkins system. Not sure about the Yanmar).

10) Get an oversized raw water strainer. The flimsy little units with port diameters barely large enough for your intake hose are poor economy. The large Groco bronze units are not that much more expensive, and give you an important margin of safety from all the garbage floating in our waterways.

Remember to clean it out every time you change the oil.

11) Check the Vetus Water-lift and all parts of the exhaust lines from the exhaust manifold.

12) Make sure that you carefully bleed all air from the system. Air-lock is a very common cause of overheating. One simple solution is to put a hose and a small petcock on the bleed valve on the top of the heat exchanger. This assumes that the heat exchanger is at the highest point in your cooling system.

13) Be careful about trapping air or other blockage in your hot water heater exchanger.

Some general comments on overheating –

According to the Perkins people, (don't know about the Yanmar) they are happy between 160-180 degrees. Most diesel people I have met prefer it to be about 180 degrees.

Put an overheating alarm in your system. Cheap insurance, as it is all too easy to ignore the temp gauge. (Replace any idiot lights with a real thermometer gauge). Make sure that the gauge is reading correctly. Don't be too impatient when solving overheating problems. Remember, on older engines, it's a high likelihood that there are multiple contributory factors leading to the overheating.

regards, Harvey May 2002

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Subject: overheating on the 3QM30?

On old raw water cooled Atomic-4s, etc. we just put in the Marsolve and let it soak for a week or more. The recirculation recommendation is to keep the Marsolve and the looped cooling water as hot as possible to enhance the chemical reaction time, just takes longer to do at ambient temperature and with non-moving fluid. You're not going to descale it all but maybe several hundred hours worth and that's still worth it.

When in a hurry we essentially collected the exhaust water into a bucket/tub, disconnected the inlet raw water hose from the seacock and ran a long intake hose back to the bucket. Ran the engine (now closed loop cooling) until the water got hot and then simply shut down. Every few hours repeated by starting, warming, stopping.

If you're well experienced with working with strong acids and their neutralization, there is always muriatic acid, etc.

Rich Hampel May 2002

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I suspect that you may have air-lock in your cooling system. Bleeding the air from the system refers to bleeding the air from the cooling system, not from the fresh hot water tank. In order to bleed the air from the system, you have to find the highest point in the cooling system (containing the anti-freeze fluid), and then let that bleed off. In order to avoid burning yourself, and to do it in a controlled manner, I suggest the following (I have the Perkins 4-108. It may be different on other engines):

1) Get a fitting for the bleed valve on the top of the heat exchanger.

2) Connect a two-foot length of highest quality engine hot water hose.

3) Attach to the fitting on the top of the heat exchanger

4) Put a petcock for bleeding the system at the end of the hose.

5) Hold the hose vertically while the engine is running

6) Open the petcock. The anti-freeze will start to come out. Let it flow until there are no more bubbles in the system.

This may solve your overheating problem. We struggled for two years with resulting new salt water pump, fresh water pump, new heat exchanger, new hoses, new thermostat, new thermometer, considered re-cutting the prop (I decided against that!), until I finally did this simple thing for a total of about $10. It solved the problem. I now sit at a constant 174 degrees regardless of the length of time that I run the engine. Hope this helps.

Regards, Harvey May 2002

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Harvey, I like this "brain storming" because one questions leads to another. You mentioned your hot water heater is located in the lazarette, mine is located under the 1/2 berth to port and I have been trying to solve a overheating problem with Sirena since day one. Could it be that it's (hot water heater) is air bound??? The first year I owned her, I had plenty of hot water through the engine. After the engine was running just a short period of time (3QM30), it would over heat at max RPM (only 2200 SOG 7kts). Last year, I re-cut my prop pitch to something less than the 18x 11.5. Now I can get 2550RPM before it over heats though I lost SOG to 6.3kts. When you mentioned hot water heater below the engine....... mine is questionable on that and since the first year I winterized it, I don't have the hot water I did the year I bought her, and even after running the engine for hours, I don't have really HOT..HOT water anymore. I must not be bleeding the system properly when I re-commisioned in the spring and this may be causing the high temp alarm sounding at max RPM...what do you think? And how should I bleed the system? I normally just run the hot water through the hot faucets till the air stops coming out.

Chuck June 2002

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We also have a Perkins 4-108. A solid, workhorse engine. (See the recent evaluation of engines in Practical Sailor). Not clear from your description which version of the heat exchanger you have. You should have one intake port for salt water, one output for salt water, one intake for the cooling fluid (antifreeze) and one output. The heat exchanger is literally that - salt water flows in and out in a number of parallel copper tubes. The copper tubes are surrounded by antifreeze. The anti-freeze transfers the heat from the engine to the salt water, hence the name Heat Exchanger. The air lock
occurs in the chamber containing the Anti-freeze fluid. The heat exchanger should be at the highest point in your complete system (i.e. it should be higher than your water heater).

In addition, you should have a large diameter plate ("clean out cover") at the intake side of the saltwater port that can be removed. Some heat exchangers have a plate at each end. This is critical as it allows you to remove large fragments of material that might get drawn into your saltwater intake. (I assume that you have a raw water strainer between the through-hull and the saltwater pump - if not, you should put one in for safety of the engine). If your saltwater impeller deteriorates, the parts

will get caught in the heat exchanger.

In addition to those four ports, and the clean out covers, there are two additional smaller ports on most heat exchangers.

One, at the bottom of the heat exchanger and closest to the saltwater intake port, is the Zinc. This is threaded into a brass/bronze cap that screws into the heat exchanger. It MUST be changed every few months. We routinely do that when we do an oil change. Failure to do this will result in serious damage to the heat exchanger by galvanic corrosion. It is hard to see, so many people fail to attend to it.

The second and smallest port on the heat exchanger is supposed to be in the center and on the TOP of the unit. It might actually be possible to mount the heat exchanger upside down. If you had a dummy car mechanic work on your boat engine, this might actually happen. This is the bleed port, to eliminate air from the closed system containing the antifreeze. This is under pressure, as all are familiar with the issues about removing a "radiator" cap (Actually, it is called the reserve reservoir, since a boat doesn't have a separate radiator). The bleed port is supposed to be at the very highest point in the cooling system, so that air will accumulate there and can be "bled off". This is most easily done if you add a small hose with a petcock to this port. Trying to loosen the threaded insert, let out air,
and then force it back into the port, while scalding your hands with extremely hot toxic fluids, in the dark, is not my idea of fun. $2-3 worth of parts solve this problem easily.

The heat exchanger is actually a simple, but critical component of your heating system. I don't know the statistics, but I will bet that improper bleeding of the heat exchanger is a major source of engine overheating. I would definitely look into that long before I started re-cutting the pitch on a propeller, changing thermostats, temp gauges, water pumps, exhaust lines, water lifts, heat exchanger, etc. (Needless to add, my BOAT mechanic changed all those things while trying to figure out why I was always overheating, before I discovered the bleed port. It was a $2,000 lesson. I realized it only by chance when a local diesel engine mechanic asked about the bleed port and told me that he always puts on a petcock to facilitate bleeding the engine. Since that time, my engine sits at a steady and imperturbable 175 degrees F.

regards, Harvey Tayana 37 Hull #84 1977 June 2002

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Subject: Perkins Engine Heat Exchanger Query

I have a Perkins 4-108 and want to make sure the "zincs" in the heat exchanger are okay. My heat exchanger (small cylinder over aft end of engine) has 3 small plugs and one large plug. Two of the small plugs (7/16") are near either end down low and the third is in the middle up high. The large plug (11/16") is on the port side near the hose connections.

When I removed the starboard small plug... no water. When I removed the port small plug, fresh water came out. Obviously no water came out of the top center plug. When I removed the large plug, salt water came out.

The small plugs are flat on the end and the large plug is hollow with threads. Am I correct to assume that the zinc gets screwed into the threads on the inside of the large plug? If so, are they a standard item at West Marine type stores?

It doesn't appear the small plugs are for zincs. Am I correct to assume so? What, then are they for?

My engine was running hot and I was worried that the heat exchanger was blocked. Clean water came from both the salt water and fresh water holes. How can I tell if it is blocked and not cooling the water properly?

Thanks for any advice! I really learn a lot from all the postings you folks make!

Bill Roberts S/V Kracker T-37 1977 Pearl Harbor, HI June 2002

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I was shocked at the price I have to pay for this elbow. Are you ready for this - $330 direct from England (plus shipping). If I buy one here in the states from a Perkins dealer it was $589. GAG.
The boot which in my estimation will be trashed when I am done is $35 versus $60 here. What I have been told is that these engines being almost 20 years old were never imported in to the US. So there were never parts brought over for them because they were not sold by US Dealers. Consequently my local dealer has never seen parts for this motor. So if you find a Perkins junkyard, try to snag an elbow as a spare.

FYI, the Perkins Elbow part number is 4133y001. They call it a connection. The gasket is 2481886 or 2481885. They call it a joint. The boot 24865264, they call it a cover.

Andy Windy Blue June 2002

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This is a great e-mail list! Thanks everyone for the great advice. I forgot to mention that when I removed the heat exchanger tube stack I took it to a radiator shop to be cleaned. I couldn't see any blockage of the tubing ID's and the outside was covered only in slime before it was cleaned. Afterwards it was clean metal. When I disassembled the heat exchanger, thermostat, raw water impeller, and raw water strainer I checked thoroughly for calcium buildup and debris of any kind. I drained the heat exchanger and engine block completely. I did not drain the hot water heater. I filled the heat exchanger fresh water side (with radiator cap) with new 50/50 Antifreeze water mix. I left the radiator cap off, ran the engine, and watched the temp gage climb to 150° then the new thermostat opened. I could tell this because the thermostat cover and heat exchanger got hot; as hot as below the thermostat and I could see water rushing by in the open heat exchanger. I ran the engine in gear at the dock at 2000 RPM for one hour. The temp stayed at 175° until I went for a ride and took the engine up to 2600RPM. The temperature rose to over 200° and the buzzer went off.

I will take "getting a different prop" off my checklist.

I will check my hot water heater for airlock.

Doug Simms Aquadesiac Tayana V-42, #108 San Francisco Bay June 2002

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I did some research last night on line and found the Bowman web site. They made the heat exchanger/tank/exhaust manifold casting for the engine that I have. The Perkins service manual refers to it as the "New" Perkins 4-108.

I looked at the i Net Marine heat exchangers and they look like only a heat exchanger. I would have to get a separate exhaust manifold and header tank to make theirs work. FYI: The Bowman Part number is PE180-3483 http://www.ejbowman.co.uk/products/pdf/marine.pdf . Go to page 2. The top photo is my engine.

Since they didn't have any US distributors listed on their web site, I called England this morning to see if there was any stock in the US. They were very nice, but there weren't any parts on this side of the pond. They referred me to Transcool in New Jersey, their distributor, (210) 869-5112. Jeanine, there, was very helpful. She arranged to have one express shipped directly from England to my house! If I was willing to wait until Mid-August the heat exchanger would be $586.00 + shipping from New Jersey. Even with express shipping from England, it is cheaper than $1100.00.

Doug Aquadesiac Tayana V-42, #108 San Francisco Bay June 2002

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Doug,
The continuing symptoms sound very much like the ones I experienced. That does not guarantee that the cause is the same, but maybe.... Do not disconnect the return hose unless you are certain that it is the highest point in the system. The air gets trapped at that point and causes an airlock. Is your heat exchanger higher than the top level of the water heater? Exactly where is your hot water heater in relationship to the engine? You may find it helpful to completely bypass your hot water heater until you track down and solve the overheating problem. If the heat exchanger is the highest point, look on the top of the heat exchanger in about the center for a small brass bolt. It has either a hex head or a square head. It is no more than about 1/4" diameter.

When the engine is cold, remove that bolt. Go to your local friendly engine parts shop with that bolt in hand. Find a brass fitting with the same thread (male) and a barbed outlet. Get a piece of black engine hot water hose that fits on the barbed end. Make it at least 2 feet long. Get a few hose clamps. Now get a small petcock that will fit on the other end of the hose. Assemble the pieces, with hose clamps on all junctions. You may have to use and extra fitting if the engine oil filter blocks your free access to the point of the bleed screw. (It did on ours. I had to get an extra small right angle fitting. It increased the cost another buck.

Thread the assembled unit back into the hole on the top of the heat exchanger. Keep it vertical with the petcock well above the highest point of the engine, heat exchanger, and hot water heater. Position the petcock in a place that you can easily reach it SAFELY while the engine is running.

Now start the engine.

Let it run at the dock for 10-15 minutes.

Very carefully - Open the petcock and see if antifreeze flows out freely.

Try not to burn yourself on the hot antifreeze. Have a small bucket handy to catch the flowing antifreeze. It is toxic to the environment and should not be dumped into the harbor. This is the first stage of bleeding. Now close the petcock.

If the engine remains cool, run the boat around the harbor, with a sharp eye on the thermostat. After about 15-20 minutes, with the engine still running, and again being very careful not to endanger yourself on the running engine, open the petcock once again, and let it flow until you no longer get any bubbles coming out. Close the petcock. Motor around the harbor a bit more, and repeat this several times.
If this is the source of the problem, this should solve it. But it requires some persistence and repeated bleeding. Don't be too impatient, and don't get too far from the dock, just in case this ISN'T the source of the problem.

While you are doing all this muddling about, you also probably stumbled upon the Zinc at the bottom of the intake end of the heat exchanger. That Zinc should be changed with regularity.

Other things - did you change the thermostat? That is a cheap part, and should be replaced. Make sure that you get one that opens at about 160 degrees F. I found that the 156 degree unit actually maintained the engine at just about 175 degrees F. This may be due to some tortuous passages in the cooling system. In examining the original thermostat, I found that it was all encrusted, so I replaced it with a new one. But initially, I used too high a temp. After cleaning the original brass thermostat, I found a calibration temperature written on it of (I think?) of 156 degrees.

It is quite simple to remove the thermostat. If the overheating continues, try popping out the thermostat and running the engine that way, without any thermostat. We did that and found that the engine stayed at about 130 degrees. I never could get it any higher (assuming that you also bleed the engine after each of these changes of thermostat). I put the thermostat back in and found a second problem was that I was too exuberant in my use of silicone gasket material on the thermostat. I put a bit too much on, and it plugged up the thermostat. It only requires a very thin film of the blue silicone gasket material.

I also assume that you thoroughly flushed out the fresh water cooling. Crud can accumulate in the internal flow system. Give the whole system a good flushing.

Did you also make sure that the saltwater flow is adequate?

Did you check the salt-water strainer on the intake?

Did you check the intake through-hull port for debris?

Do you get an adequate flow out the stern exhaust pipe?

Are the exhaust hoses fully patent, or have they gotten soft and old with age and partially collapsed?

How about the various engine hoses? Are they in good condition?

Check the flow through the transmission cooler.

Change the "radiator" cap (actually, it's called the coolant reservoir cap).

This ain't rocket science. It is two flow systems, one cold ocean salt water, and one an internal fresh water system. Their only interface is the heat exchanger. Check each system, the fresh and the salt, and check the heat exchanger.

If it is of some scant consolation, we had to screw around with our system for several months before we realized that the major source of problem was failure to adequately bleed all the air out of the system. A lot of mechanics seem to skip that, because the location of the bleed screw is damned near inaccessible, and when you do try to loosen it, it tends to fall into the deepest part of the bilge, and the hot antifreeze burns your hands when trying to thread it back in place. The petcock is a simple solution.

There was one really puzzling aspect to our experience, which also resembled your experience. When we slowly started to improve performance, I could run it at the dock for quite a while when in gear, and the engine didn't seem to overheat. But when I was motoring around the harbor, after about 30-45 minutes it would climb up to about 210 degrees F. I would have thought that running the engine in gear at the dock would impose an equivalent load as motoring. But apparently the load is not the same.

At risk of provoking the wrath of the gods, we have not had any overheating for the past two years.

Harvey J. Karten, M.D. June 2002

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Subject: Help, I need a Perkins part.

My Perkins 4-108 has a nasty over-heating habit. I have replaced and checked the easy stuff like the thermostat, the sea water impeller, and removed the copper or bronze tube stack. I also cleaned the raw water strainer.

I noticed a lot of corrosion at the heat exchanger casting nipple to the thermostat. I was wondering if the internals of the heat exchanger casting have corroded enough to not direct the flow through the tube stack. The seawater coming out of the heat exchanger is just luke warm even though the engine temp is +200°F. I checked with a local Perkins diesel shop and he thinks that my prop is too big. The engine will not turn faster than 2750 RPM in gear. Does anyone have any experience with the heat exchangers corroding away? I did see several similar vintage Perkins engines with new heat exchangers on the internet when I did a search.

The quoted cost for the Perkins heat exchanger was $1800.00 and a Bowman unit was only $1100.00 (cheap). The units at the i Net Marine site don't look anything like the combo exhaust manifold/heat exchanger unit on my engine.

Doug Aquadesiac Tayana V-42, #108 San Francisco Bay June 2002

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I'm experiencing exactly the same problem with our 4-108. Have gone through all the procedures you have. Temp gauge goes into the red if run for any length of time under load at 2500 RPM or over. Two mechanics have looked at it with no ideas that have worked. If I run up to about 2400 everything is fine, but still running hotter than thermostat is set for. Around 2200, will stay at 180 continuously. Any ideas out there?

# Bill Rohde s/v Jubilee Van 42 PH Cutter June 2002

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Subject: Overheating at higher RPM, but not at lower?

Hi Harvey:

Thanks for the suggestion, but the mechanic at our yard did check the revs last year and the tach was petty close.

We have a 17" Max prop which I've adjusted three times, including a shallow pitch (can't remember how shallow I went) where I wasn't able to power much over about 4.5 knots (changed that one after about 4 miles of motoring). The overheating problem hasn't seemed to be affected much by my pitch changes, more by the RPM.

We've replaced the raw water impeller. We've pulled and cleaned the exchanger. We've changed hoses. I even replaced the water heater (but for different reasons - the 10-year old one we inherited started leaking). Checked the actual engine temp with a gun to ensure that the gauges were reading right -- they are. The overheating remains.

BTW - we're also not very happy with speed under power, which is a function too of RPM’s that I can run without overheating. In flat water, I can only run somewhere between 5.6 & 5.8, which is what I easily did on our Van32. Seems like the 42 ought to easily power between 6.5 & 7. On that front, I had about come to the conclusion that the Van 42 needs about 75 horses -- that the 50 horse Perkins is just not enough, but maybe I'd feel differently if I could run the revs up a bit more.

Bill Rohde June 2002

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Hi Folks,

I had the same problem with a V-42 and a 4-108. I did everything I could with the water system, heat exchanger, prop pitch (16 inches fixed, changed it from 11 to 10 and then to 12 to see what difference it would make), etc and got the same result - couldn't go over 2200 rpm without overheating and at that RPM could barely get 6 knots and much less than that with any kind of head wind. I talked to one guy who bought a second heat exchanger and installed it in parallel with the first and that solved his problem. But I came to the same conclusion as Bill - a fifty horse motor is not enough - especially one that develops its fifty horses at almost 4000 RPM. Its too noisy and vibratey at anything near that speed and it seems as if it would wear out quicker because it has to run at such high revs. At the 22-2400 RPM range we have been talking about that engine only is putting out about 30 horses. So I changed out the engine (in process) to a Perkins-Sabre M65 (same footprint) which develops 65 horses at 2400 RPM. This will allow me to run a serious alternator (250 amp) at very low RPM as well as develop enough horses at lower RPM to push the boat along at something approaching hull speed using a bigger prop. I'll let you know the results.

John B. Van Zwieten July 2002

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Hi V-42 Owners,

I have solved my overheating problem by adding a second heat exchanger. I will post pictures on my web site in a few weeks. I had already received the replacement Bowman unit and I am running out of time before my trip, so I used it rather than order a different type.

I spoke to the Technical Expert at Bowman about the capacity of the PE180-3483 heat exchanger. He said that the heat exchanger was designed to get rid of 50 horsepower equivalent in heat. As I remember my physics of the Diesel engine from school, a diesel is efficient, but not 50% efficient. The Perkins consumes 3.6 gallons of diesel per hour at 4000 RPM and full throttle and diesel has a heat content of 145,000 BTU/Gal. That totals 522,000 BTU/hr or 205 horsepower. Since the engine's output at 4000 RPM is 51 horsepower, that leaves 154 horsepower or 392,000 BTU/hr to get rid of in heat (by the second law of thermodynamics, conservation of energy).

I put the second one in series in stead of parallel because the sea water was still cool coming out of the original heat exchanger. I also noted that the water routing on the heat exchanger was set up for parallel-flow rather than counter-flow. What I mean by counter-flow is the cold seawater should enter the same end of the exchanger as the fresh water exit. Heat exchangers are more efficient with counter-flow routing so I re-routed mine to counter-flow. I used just fresh water only to check for leaks and the engine would run at 150°F for 45 minutes at 2600RPM in gear. Bowman used aluminum for the casting touting it as "corrosion resistant". Nothing could be farther from the truth in the marine environment. Aluminum is right next to zinc in the galvanic table so the aluminum casting will disappear just like zincs do. I used a 3/1 antifreeze/water mixture in the freshwater side to reduce the corrosion of the aluminum. With the antifreeze coolant, the temperature stabilized at 175°F after about 30 minutes at 2650RPM underway. Since the water temperature was 64° this indicates to me that 2 heat exchangers are still marginal when you use antifreeze.

I was able to get 6.8 knots @ 2650RPM going into 10 knots of wind and 7.2 knots at 2750RPM going with the wind. I have to agree with John that the Perkins 4-108 is probably too small for the V-42.

Doug Aquadesiac Tayana V-42, #108 San Francisco Bay July 2002

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My tach (as I believe most diesels do) comes off the tach. Also, I can only get 2200 RPM indicated on mine at full throttle, so am not sure I trust it until I can find an optical tach to borrow sometime so I can verify it.

By the way, for anyone concerned with the overheating issue, I solved mine. The symptom was that it would run fine for 10-60 minutes, then overheat (faster at higher throttle than at lower). I pulled my heat exchanger, filled it up with Lime Away (purchased at the local Longs drug store) and left it over night. By morning, the foaming had stopped and there was 1/4" - 3/8" of what I think was calcium carbonate sludge in the bottom of the bucket. But it back together and now I can't get it to overheat even at full throttle.

For the record, removing and replacing it was not as difficult a job as I had feared.

Fair winds - Dan Best September 2002

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Dan,
The Perkins 4-108 has two methods for reading engine RPM. The major and most common method is that described by Dan Best. It is a direct take-off from the alternator. The second method is a mechanical take-off near the forward end of the engine on the starboard side. It is a small 1.5" cap just above the engine sump. It requires a special gauge, and I have never actually seen one in operation.

The output from the alternator to the Tachometer is determined by the size of the pulley on the alternator. If you change the alternator from the undersized Delco-Remy originally provided, make sure that they put on the correct diameter pulley drum. If you have the typical Tachometer from Teleflex commonly provided with Perkins engines, you will find two adjustments on the back of the meter. A large black one with a screwdriver slot and with a pointer to A, B and C. It will probably be pointing to C. These selections refer to the settings required for each of several different diameter pulleys (and alternators?). This sets the general range. But you also have to get an external optical tachometer to fine-tune the calibration. There is a smaller hole up and to the left of the adjustment
screw mentioned above. It requires a fine jeweler's screwdriver.

Using an optical tachometer, (a small strobe, a piece of reflective tape on the main drive of the engine and a digital multimeter), and extreme caution not to get too close to the spinning engine, generate a performance curve for your engine. This generally requires two people. Take a reading of the tachometer in the cockpit at different RPM’s from about 500 to 2,500, while also reading the values on the optical tachometer. This will provide you with a calibration curve for the tachometer/ alternator combination. If the values are less than 5% apart at all RPM’s, you should leave it alone, and be happy. In our case, they were off by slightly over 20%. Using the small jeweler's screwdriver, adjust the small screw visible through the small hole in the back of the Tachometer. This only seems to bring the range into approximate value, and I have to check it further, but I have the impression that it changes the offset value uniformly across the full range, rather than changing the percentage. (i.e. it will add 300 RPM across the full range, rather than subtracting 20% - that is, increasing the reading at 500 to a new value of 600, while increasing the value of 2,000 to a new value of 2,400. Instead, if you increase the reading at 2,000 to 2,400, it will increase the reading at 500 to a new value of 900. ) If this is true, (and I think it is), I decided to increase the reading for the high RPM for maximal accuracy to avoid over-revving the engine. Hope this helps.

regards, Harvey September 2002

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By moving the water heater out of the heat exchanger loop our boat realized a 15% increase in the top, continuous speed. The following web page shows three graphs of the engine temperature versus boat speed. The first is the original condition, the second with new raw water pump, and third is with the water heater moved to the thermostat by pass.

www.sankaty.homestead.com/speed.html
I am happy because our good old 1980, 32 HP, Universal 5432 no longer overheats.

Markus Ritter October 2002

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My 3QM30H with raw water cooling (i.e. no heat exchanger) runs at 170 degrees at cruise RPM. This seems too hot. Don't want the salt to come out of solution and clog engine cooling passages. What temp do others see for this setup?

Kendall Bailey October 2004

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A rise in temperature causes a corresponding rise in the ability of water to hold any given concentration of salt, i.e., hot water can hold more salt than cold water.

Voyager October 2004

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Change to a thermostat that opens full at 135 degrees to lessen precipitation of carbonates.

Even with a 135 degree thermostat there will be zones inside the engine (exhaust manifold & head) that will exceed 150 degrees; 150 degrees is the point where carbonates begin to drop out of the seawater and adhere to the internal passages.

Plan to 'pickle' the engine yearly with an organic 'descaler' such as RydLyme® or Marsolve®. Try not to use an inorganic acid such as muriatic, etc. as they will also remove base metal.

Rich Hampel October 2004

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Best advice I can offer versus 'over-heating problems' is to take a bucket and stopwatch and go to the exhaust port at the stern, run the engine at a specified rpm (as per your manual) and see if the
flow rate (gallons per minute per rpm level) matches the spec. The cooling water flow spec should be something like: 4 gpm @ 2000 rpm, etc. If you don’t have the spec. flow rate coming out the back end, then look for obstructions: broken pieces of impeller, the exhaust manifold starting to degrade internally (can give 'transitory' problems), etc.

If the flow rate matches spec. then you have a 'fouling problem" or an air blockage .... and it may be 'in the engine' (need for 'pickling') instead of the exchanger (unless you filled with distilled water) etc. If all that investigation fails to find the culprit, then ask yourself if the engine is overfueling (high-pressure pump) or is the engine 'lugging' (high load + low rpm --- wrong prop pitch).

Exhaust manifolds are cast iron and although a good metal for such service, sometimes degrade by having huge rust 'platelets' of rust break loose from the internal walls and temporarily block the flow passages (they also form pin holes and leak water into the combustion chambers and ruin the engine .... lets not go there). Next time you have an overheat problem, quickly and without burning your hand simply and quickly run your hand over the engine and the exhaust circuit seeking the 'hot' spot. You don’t have to actually touch the engine, just get close enough to feel the heat radiation. Compare when the engine is running 'normally'. An alternative is to go to a dairy supply and get 'Temple Sticks" .... colored wax 'crayons' that melt at different temperatures .... rub the wax at varying locations and watch to see which 'color' melts first, etc. ;-)

Rich Hampel May 2005

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Subject: Overheating Perkins 4-108

Harvey, John, Rich, and Tad,

Thanks for the responses. I am deeper into engines than I have ever been before. A couple of questions for you, collectively:

What is pickling my engine. I can grasp the thought - something like cleaning the head with vinegar - can I do that?

What type of petcock do I use? Would it be available at an automotive store? Would I install it on the forward side of the heat exchanger?

If any of you have a 4.108, where is the drain for the cooling system. The best we could do was disconnect the lower hose on the heat exchanger (feed line) for the water heater.

If any of you have a T-42, what size prop do you have? Thanks.

Jon May 2005

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Hi Jon,

Hope you can track down the overheating problem. Harvey has some very good ideas and has lots of experience with this. As far as checking for barnacles on the prop, there is a much easier way then going overboard. When the prop is totally, absolutely clean (just put back in the water - not a week later...), do an RPM test. If in your slip, place the engine in gear and take up the slack in your mooring lines. Then quickly go to full throttle and note the RPM. You can do this in reverse too. When you check a few months later and see a loss of 200 RPM's, you have a fouled prop (and most likely a fouled hull). If you see more than a 200-RPM loss, best to clean the prop before getting underway. You may even have trouble backing out of your slip. Reverse thrust is the first thing to go. To compare prop pitch, check the FTP site for my info on Autoprop. It contains a lot of information on prop performance on V-42's with various props. Note that your transmission ratio is critical when comparing one Perkins-equipped boat to another. If you have a 3-to-1 ratio, my information will be totally irrelevant. If close to 2-to-1, you should be getting around 2450 RPM in your slip. As far as cruise RPM, John and Harvey just reported that they normally use 1800 to 2000 RPM. My V-42 is the same. I am guessing that John and Harvey have Hurth transmissions with 1.88-to-1 drive ratios.

A "New" Perkins 4-108 (Bowman heat exchanger) passes 5 gal/min of water through the exhaust system at idle (700-750 RPM). I conducted this test on my boat with a properly functioning cooling system. Pictures of most standard models are at ftp://tognews.com/Perkins_4_108_Models . The “New” was the last model built. Models built previous to that engine are often called “Lowline” or “Highline” engines due to heat exchanger configuration. It sounds like you have one of the older models with a different cooling system. It should be as good if not better than the Bowman setup, which is a little undersized for a Perkins if everything is not ideal.

Has your boat been in the water for a year now with no bottom cleaning? Fouling can cause sluggishness. And it can happen quickly. I once stayed two days in a marina and lost half a knot (at cruising RPM). That evening, I cleaned the bottom and gained all that speed back. It was just a light coat of slime. I wouldn’t have thought fouling could occur that quickly or cause such a dramatic drop in speed.

Wayne V-42 C/C RESTLESS May 2005

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