Overheat Mystery

[pries]

I have an OMC 4cyl in a 1987 Starcraft Islander that runs about 200 degrees. Impeller is good. Replaced temp sensor and temp gauge. The OEM thermostat is rated at 170 degrees. Tested that in hot water with thermometer and it does start to open around that temp and is completely open about 180 degrees. Its never died on me but I would like to see that motor run cooler than 200 degrees. Anyone know what's normal for those engines/boats? And what else to be looking at?

 

[southkogs]

Are you sure the gauge is reading correctly?

 

[Scott Danforth]

first, check the temperature with an IR thermometer. dont rely on a 35 year old $3 gauge

 

[hugh g]

Normal operating temp is about 160-170 degrees. With a new gauge & sensor something else is going on. If you have a spare impeller change it out & see what happens. Hook your boat up to muffs & remove the triangular cover for the water pump. Start the engine & look for a pee stream from the vent tube on the water pump cover.

 

[Lou C]

Yep make sure the impeller is pumping and remember that these open systems need a lot of cool water in and hot water out; anything that impedes the in or out will cause overheating. You can have leaks on the intake side (water tube gaskets; plastic transom hose nipple) or blockage on the exhaust side (exhaust manifold and elbow cooling passages blocked by rust). I always install the whole kit (impeller, metal cage & wear plate) and use OMC original parts. If you use aftermarket do not mix and match, don’t put an OMC impeller in a Sierra housing or vice versa. Use all one or the other. I have found that as long as not starved for water they easily last 3-4 seasons.