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Discussion Starter #1
We are having problems with our 1986 m25 universal Diesel engine cooling. Running at idle for 10 minutes causes a steady rise of temperature to 200 and still increasing (at which point we kill it). All connections to heat exchanger (part 299049) are cold to the touch after this period, even though coolant is hot. Replaced thermostat, no blockages in heat exchanger (gravity pulls coolant from manifold out other end of heat exchanger). Was able to pump coolant with siphon pump from “to water heater” hose to the thermostat cap. Hot coolant from thermostat not seeming to travel to heat exchanger even though no apparent blockages or air locks. Coolant comes out of the thermostat pet **** when bleeding. Possibly faulty coolant pump? Any other causes for this problem?
 

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Learning the HARD way...
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This is the second time this month that I've had to post this;

SERVCE BULLETIN
DAT; 5 August 1991 BULLETIN NUMBER: 195
Model Universal M25, MZSXP, M30, Model 5424 and 5432
SUBJECT= Heat Exchanger #299049
Early versions of the above model Universal propulsion engines were configured with a two inch diameter heat exchanger P/N
#299049 where as 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 r.p.m.

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:

l. Supply hose to the raw water pump. Hose material should be wire reinforced so as not to collapse due to pump suction. This hose should be neatly routed so as to avoid sharp bends or possible kinking that would obstruct water flow.
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. (Example — pump inlet l/2 N.P.T. standard nipple will accept 3/4 I.D. 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 engine’s 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) originally supplied with the engine with the three inch diameter heat exchanger‘Universal incorporated on later models (P/N #299835).
_ Revised
January 1992
 

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Discussion Starter #4
Solved the problem. It was an air pocket that developed in the coolant pipes leading to our water heater. Disconnecting it from the system finally lead to temperatures at normal levels. Our temperature never exceeded 160 F afterwards. Thank you everyone for your quick responses. Feel free to ask any questions, I will be happy to answer.
 
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