Runs cool on muffs but overheats in water- 1991 Force 50

[Bearmanpaul]

I have a '91 Force 50 that I've been playing with for a while- new head gasket (was busted), new water pump impeller. The thermostat has been removed by the previous owner, probably because he knew there was a cooling problem. On muffs, it runs cool and plenty of water is being pumped- it comes out the plug hole at the top of the head when I remove it, the idle relief ports, and down by the prop. Then when I put it in a bucket or on the lake, it overheats almost immediately. The head gets to 212F measured with infrared thermometer, indicating there is water in there that is boiling. This tells me that the water is getting to the head and there is something blocking it farther down. However on muffs with the thermostat out, it only gets to about 100F. The back pressure on the exhaust from being submerged is stopping water flow. Has anyone had this problem, and if so what is it?

 

[GA_Boater]

Muffs don't count when looking into any cooling problem unless you have a really long hose to cruise on the lake.

Didn't forget or misplace the impeller drive key? The water tube is in both the pump housing and powerhead port? Are you dunking the motor deep enough in the bucket or lake? Water has to be above the pump.

 

[Jiggz]

On muffs, it's most likely the spigot pressure provides the cooling rather than the impeller. The fact it stays cool indicates there are no blockage in the cooling ports. Re-check impeller and do test runs without the t-stat until overheating is gone.

 

[jerryjerry05]

Pics of the pump with anything that is part of the cooling system.

I's possible the tube seal at the top has gone bad?
Put a hose over the tube and turn the water on.
Tilt the motor up turn the water on and watch up inside with a light or bore scope.

Test the thermostat?