Overheating Causes
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Note: 05 August 1991
Service Bulletin Number: #195
Model: 5432
Subject: Heat Exchanger #299049
Early versions (1978 to 1983) of the Universal 5432 or Westerbeke M40 marine propulsion engines were configured with a two inch diameter heat exchanger P/N 299049. Later and current production models have a three inch diameter heat exchanger P/N 299835.
Complaints have been received from the field on some of the above early model engines regarding high water operating temperatures (above 190 degrees F). Complaints of overheating when operating the engine at high or maximum rated engine RPM.
These complaints are possibly related to the heat exchanger size used on these early models. One should keep in mind that there are other components and areas of the engine's cooling system that could cause or contribute to high operating temperatures and overheating. These are:
1. Supply hose to the raw water pump. Hose should be wire reinforced and routed to avoid sharp bends.
2. The raw water supply hose inside diameter should be as large as a standard hose nipple will allow the raw water pump to accept without bushing up. i.e. pump inlet 1/2" npt standard nipple will accept 3/4" ID hose.
3. Raw water pump internal wear and impeller fatigue.
4. Reduced flow of raw water and/or fresh water through the heat exchanger due to corrosion, scale or debris inside the exchanger.
5. Internal corrosion of the water injected exhaust elbow causing raw water flow restrictions.
6. Domestic hot water heater improperly plumbed into the engines fresh water circuit.
If these areas 1 - 6 have been inspected and any faults that are found are corrected and overheating still occurs, it is recommended that the operator consider replacing the two inch diameter heat exchanger P/N 299049 with the three inch diameter heat exchanger P/N 299835.
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Sankaty moved the water heater from in series with the heat exchanger to the Thermostat by pass circuit. Click here for a graph showing the dramatic improvement. that cost less than $30 in parts. The max temperature is now 185 after 15 minutes at top RPM in still air and seas. After one hour at 7 knots its still only 188 degrees.
Sankaty would still like to get it down to 165 degrees; so she may end up ordering the three inch heat exchanger also.
Others have found that at high speed the water covered the exhaust and the increased back pressure caused over heating. They found that adding a piece of hose to raise the exhaust solved their problem. On my boat the water comes right up to the exhaust, but does not cover it.
In addition some have found that their exhaust elbows have very excessive carbon build up that is difficult to remove and often cured by replacing the elbow.
Don't forget to tighten your fan belt as it drives the fresh water pump.
Yet another reported that barnacles on the prop caused overheating.
Another said he disconnected the salt water hose from the thru-hull fitting and place it in a bucket mixed with one part swimming pool acid with five parts fresh water and run it through the the engine. Let it stand for a few minutes then run the remainder of the acid mixture. Reported it worked great.
