1998 5.7L Overheating

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drwhitesr

Recruit
Joined
Jun 30, 2012
Messages
2
I have a 1998 5.7L MerCruiser with a Alpha 1 Gen II that overheats when running on plane. If I reduce the throttle to idle it will cool down and the warning alarm will shut off. I replaced the impeller in the lower unit, and the thermostat. No change. Checked the flaps in the exhaust to make sure they were not stuck closed. They are not. I checked the risers to see if they were clogged with rust and debris. they appear to be OK. Any thoughts would be greatly appreciated. Engine and drive only have 243 Hrs on them.
 
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HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Re: 1998 5.7L Overheating

drwhitesr said:
I have a 1998 5.7L MerCruiser with a Alpha 1 Gen II that overheats when running on plane. If I reduce the throttle to idle it will cool down and the warning alarm will shut off. I replaced the impeller in the lower unit, and the thermostat..
Click to expand...


Howdy, Welcome aboard,

You might check the oil/power steering cooler for debris. If it's clogged, or partially clogged you'll get overheats at high power settings.

Sometimes impeller fragments can also lodge anywhere between the raw water pump and the transom and/or the hose that comes from the the transom and goes to the t-stat housing. (or in the housing itself)

With this type of clog, you may get enough flow to cool the engine at lower throttle settings but not at full or near full throttle.


Regards,


Rick
 
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