slow overheat

[lynnboy021]

ok guys when i am at idle (600 - 850) the motor slowly overheats if i am at 1200 rpm or more it does not even go over 50 and the motor also does not overheat on plane. i checked for cloges and theres none i got a new impeller kit just to make sure it was not that and it still overheats slow 82 mercruiser 120 with alpha 1

 

[JustJason]

Re: slow overheat

lets talk actuall temps here.

What temp are you considering "overheating"? And are you using an actual pyrometer to verify the temps, or are you relying on the boats gauge? does the boats gauge have numbers on it or is it one of those green/yellow/red gauges?
What do you mean by it does not go over 50? 50 degrees?

 

[newcdnboater]

Re: slow overheat

Sounds to me like the water pump is not moving enough volume at low RPM.
Perhaps the belt is slipping a bit and at low rpm the pump is not turning fast enough.

 

[jerryjerry05]

Re: slow overheat

Make sure it has a thermostat.Then clean out the riser.J

 

[lynnboy021]

Re: slow overheat

sorry ya when i am at hire rpm or plane it will not over heat and it does not go past 50 degrees.. I took off the thermostat to see if it will help the problem but it does not at idle it will go to 265 i think thats the highest it goes so when that happens i have to go to high rpm to go back to 50 degrees

 

[thannah84]

Re: slow overheat

50 Degrees is way way to low....Sounds almost like there is an automotive temp gauge in your dash (They read backwards if installed in marine apps) Don't know why, they just do???? I would say get a temp gun and measure the temps at the thermostat housing and manifold at low and high rpms, if they are in spec, it has to be your gauge or wiring from sending unit to gauge. You can check your gauge by shorting the wire from sending unit to engine block (Or ground) if it goes all the way to hot, your gauge is working correctly. You can also do this at the gauge by shorting the sending unit pole to the ground pole on the back of the gauge. My bet is that it is somewhere between your temp sending unit and gauge. Also, take an ohm meter and check your temp sending unit per the manual...

 

[danond]

Re: slow overheat

1: pull all your engine water hoses and drain them along with removing all the drain petcocks, fish around in them for garbage.
2: replace the thermostat with the CORRECT ONE. You have the wrong one, or the one you have has failed
3: put it all back together, run it on earmuffs in the driveway and watch the temp. IDLE ONLY.