1981 9.8 Running Hot

[JDusza]

Slowly clearing up an overheating condition on a 1981 9.8.

Replaced bad water pump impeller. Cleared water lines. Flush line completely blocked, cleared out.

When I put the thermostat in, the temperature rises dramatically. The thermostat opens at 143 degrees F. Is this the correct spec for this thermostat and engine?

Thanks,
J

 

[carholme]

Re: 1981 9.8 Running Hot

Parts Listing:

http://www.crowleymarine.com/mercury-outboard/297.cfm

See item 31 under CYLINDER BLOCK AND CRANKCASE


Gerry

 

[CharlieB]

Re: 1981 9.8 Running Hot

Stat is operating correctly

Check temp of the exhaust cover, it should remain cool, if it is heating it may have quite a mineral accumulation between the exhaust cover and exhaust plate. Remove and clean as a restricted flow here will seriously reduce cooling of the motor.

 

[JDusza]

Re: 1981 9.8 Running Hot

Thank you, Gerry. This is the thermostat I put in. I tested it first and it operates right on target. I put it back in tonight and ran it. The discharge water temp is abut 150. I guess I'm ok.
Thanks again,
J

 

[JDusza]

Re: 1981 9.8 Running Hot

Hi, Charlie,
Exhaust cover temp seems to follow water temp. I had the exhaust cover off and did clean up some mineral accumulation. Wasn't too bad. I did find a mass of gunk that looks like gasket sealant blocking up the "Flush" port, right up to the engine block. After this was cleared out, the water flow is much stronger. And, temperature lower. I tested the thermostat again and it operates right on target at 143. I decided to put the thermostat back in as it appears to be in spec. The water exit temp is about 150 when cruising, hotter at hot re-start. I'll keep an eye on it, but I think that blockage may have affected a circulation port in the bottom of the block (?)..... I am trying to avoid splitting the block from the exhaust housing.
Thank you,
J