50 hp Overheat, Need expert advice.

[ttirb]

1985 50hp. No problem at idle. (140-150). Overheat alarm goes off around 3000 rpm after a few minutes (on lake). Temperature at the top of the head 170-180 (infrared) Have replaced water pump (twice), themostat (tested), head gasket (good compression). Have pressure flushed engine from the w/p pickup tube at the gearcase, no blockage. Replaced gaskets in the lower exhaust housing. Now suspect possible demonic posession. Has anyone else out there ever run into something like this ??? Will soon need therapy.

 

[Silvertip]

Re: 50 hp Overheat, Need expert advice.

Bypass (poppet) valve not opening. This works in combination with the thermostat. The thermostat keeps engine temp up at idle and off idle rpm. As rpm increases the bypass valve opens to allow more cooling water around the thermostat. It's probably stuck shut.

 

[Willyclay]

Re: 50 hp Overheat, Need expert advice.

I'm no expert like Silvertip, but I had an experience like yours. My 1962 Johnson V4 75HP would indicate an overheat (light) after a couple of minutes at WOT. Never did actually overheat to my knowledge. Did the impeller, T-stat, poppet valve replacement thing with no improvement. Also pulled the head covers off and cleaned out the scale from saltwater. Finally, replaced the overheat sensor and the problem went away. Good luck with yours!

 

[tashasdaddy]

Re: 50 hp Overheat, Need expert advice.

seeing you tested infrared, i agree the poppet is not opening. there is not enough flow. when i do a tstat i do the poppet also. may aas well while you are there.

 

[ttirb]

Re: 50 hp Overheat, Need expert advice.

Checked poppet, moves freely. Now I am wondering if the spring is incorrect.