87 mariner 60 hp thermostat?

[Tylerevenhuis]

Hey all I have an 87 mariner 60 hp outboard that when running at wide open throttle will set off the overtemp alarm. My repair manual says that can be caused by a stuck poppet valve or bad thermostat, but doesn't say where they are. I found what looks like the spot for them under the exhuast manifold cover but I'm hesitant to take that off. In my searching online some people are saying motors in this vintage don't have thermostats or poppet valves at all and i am unable to find them in a parts breakdown using my serial number. I was wondering if anyone has any experience with these or has had the problem of the motor only overheating at wot and running fine at lower rpms? Any help would be appreciated.

 

[Tylerevenhuis]

I should add the serial number is 0b188406

 

[schematic]

Inspect the w.pump impeller. You are probably overdue....

 

[Tylerevenhuis]

Just put a new one in. I can now also confirm that there is not a thermostat or a poppet valve. The exhaust cover and the bolts holding it on look like they have factory paint on them so I'm assuming that has never been taken apart. So I took the exhaust cover off and while there was a place for both a poppet valve and a thermostat neither of them were there. So I'm assuming this motor came without those parts. While I had the exhaust cover off I didn't see any bits of an old water pump or corrosion or anything like that. It was all very clean. I put a garden hose to it and flushed out all of the passages and didn't get anything out but water so I'm assuming the passages are clean as well. So now I'm still stuck with the problem of over heating only at high rpm. Any thoughts or advise? I'm lost.

 

[tommarvin]

" you just put in a new one in"did you install a new water pump impeller<?
Do these motors have a water pump water stream out of the motor.showing it working?
A Thermostat would not be under the exhaust cover its at the top of the head.Two bolts hold it down.
I think the overtemp alarm is broken and lieing to you.
Put the muffs on and point a IR temp gun ant the top of the head is it really overheating?
Our force 125hp got to 180F and it was overheating.T stats open about 140F
Fun fact when we got our boat with a force 125hp it would overheat alarm at low rpm Means low water flow, the owner said to speed up when the overheat alarm goes off to cool her down,high water flow, I cant believe we still bought the boat.

 

[Tylerevenhuis]

Yes I replaced the impeller housing base plate cup and all the gaskets. And yes the thermostat and poppet valve are under the exhaust cover housing if they had been there from the factory, but since all the paint on the bolts and the exhaust cover looked to be original I'm assuming this motor didn't come with a thermostat or a poppet valve from the factory. I took the boat out today and still the same problem of overheating and higher rpms even after flushing the water passages. I didn't take a temp gun with me today because I was with the wife and kids, but I'm leaning toward a temp sensor. Any other thoughts or advise would be appreciated.