1990 150GT Johnson Overheat

[ETC_Val]

Im boat shopping atm and just ran a 90 johnson 150GT on the muffs, after 5 mins the overheat alarm sounded and it entered SLOW. The tell tale stream was not hot but cold and felt just as cool as it did straight out of the hose prior to motor. This sounds like a simple fix, Im thinking thermostat due to tell tale being so kewl of water. Any advice is greatly appriciated, btw compression was 104-108 on all 6 cylinders and spark was sat as well. If there is any advice on the GT150's Ill take that too, just trying to make sure I dont get ripped off. Thanks again.

Submarines once,
Submarines twice,
You know the rest.

 

[emdsapmgr]

Re: 1990 150GT Johnson Overheat

You need to determine if it is overheating or not. The thermostats should open at 143 degrees, which would mean 150 temps are normal. The overheat comes on at 212 which is hot. Could be a bad sensor in one of the heads. You can check this with a laser gun to be sure. The engine should pump somewhere around 6-8 lbs at idle. If you think the pump is working and it is not a sensor, replace both thermostats. Make sure the pressure relief valves are not melted, and that they will function properly. Compression sounds fine.

 

[dajohnson53]

Re: 1990 150GT Johnson Overheat

How fast were you running it on the hose? When the alarm sounded, did you touch the heads to see how hot they were?