120 hp force over heat

[bozgolf]

120 hp force year I think is 1990. About 2 yrs ago was going through idle zone out to the lake I go to the overheat horn/beeper came on turned motor off let it cool down and never came on again the rest of the day. Changed the impeller and did not happen again until yesterday. It was about my sixth time this year I took boat out through idle zone which 1/2 mile long ran at open throttle for about half an hour then went back to an area for fishing where you have to idle no wake and over heat hor/beep came on about 10 mins into idling. Let it cool down while trolling back. After engine cooled down started enginge overheat did not come on again. Both times I did see water coming out of the outlet ports. any help please.

 

[pnwboat]

Re: 120 hp force over heat

Have you changed the thermostat?

You can test it by placing it in a pan of hot water and measure the water temp. Slowly heat the water up and note at what temp. the thermostat opens. The thermostat should have the temp. rating stamped on it. Generally, the 4 cylinder motors used either a 130 or 143 degree thermostat, or somewhere in that general range. If it's opening at a higher temp., then I would replace it.

 

[john from md]

Re: 120 hp force over heat

Many of the overheat detectors on these old engines have deteriorated. Go to Harbor Freight and buy a handheld laser thermal tester. They are about $25. When you are out running, have someone aim the laser beam at the head for each cylinder. This will give you a digital temp reading and you will know whether you have a real problem or a bad indication.

My 85hp runs about 140 degrees at WOT measured at the head. My overheat detector, which was supposed to be a 180 degree version, was coming on 40 degrees below design temp. When I looked it over, I found it had small little cracks in the insulation.

You can buy a cheap Sierra temp gage and sender unit for about $35.

Regards,

John