Overheating?

D

dbleau

Recruit
Joined
Sep 2, 2007
Messages
2
I have a 1980 150 Johnson. There has never been a problem with it until now. The warning buzzer will go off if I idle for more than a few seconds. It does not go off at cruising speeds and will go away after shutting down the engine for 5 to 10 min. I assume this is an overheating problem and sounds more like a pump problem than a thermostat. Any ideas?
 
Silvertip

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,762
Re: Overheating?

Could be either but I lean toward thermostat. If it were an impeller, the problem would occur at wide open throttle as well since that's when the engine is working the hardest. If it can't handle cooling duty at idle it certainly couldn't at wide open throttle. Above about 2500 rpm the bypass valves open to allow extra cooling water to flow through the engine. If that weren't happening (bad impeller or bypass valve) the engine would overheat. The thermostat controls water flow at idle and low speeds. If it's stuck closed or simply failed, you have an overheat condition but as you speed up the bypass valves open to provide the extra water.
 
D

dbleau

Recruit
Joined
Sep 2, 2007
Messages
2
Re: Overheating?

Thanks, I didn't know about the bypass. It's definitly easier if it's just the thermostat.
 
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