3.7 mercruiser gets hot above 2500 rpm

[w1]

at 2000 rpm I can cruise all day, 3000 rpm starts getting hot in 6 or 7 minutes, any advice would be helpful, 1982 185 h.p. mercruiser model 485 4 cyl, with ford head. Thanks. W1.

 

[Primo321]

Re: 3.7 mercruiser gets hot above 2500 rpm

Check your impeller/water pump. Could be sucking just enough water in to keep the engine cool at low speeds. How hot is hot?

 

[w1]

Re: 3.7 mercruiser gets hot above 2500 rpm

new impeller installed. 210 to 215, at that point I reduce speed, this does have good anti-freeze in block. will it hurt to remove thermostat and test run motor to see if anything changes?

 

[stonyloam]

Re: 3.7 mercruiser gets hot above 2500 rpm

Could be blockage in the heat exchanger.

 

[north alantic]

Re: 3.7 mercruiser gets hot above 2500 rpm

When you replaced your impeller, did you check you keyway that holds your impellor in place? i have a same motor, last week, experienced same problem, @ 3000 rpm, i could cruise all day, above 3000rpm my motor would get hot.i had installed a new impellor before the boating season,what it turned out to be, was my impellor keyway was slipping , once i figured that out, ran perfect for the remaining season.

 

[w1]

Re: 3.7 mercruiser gets hot above 2500 rpm

I ran the motor at the dock this evening, the water line going into heat exchanger is cool to the touch, heat exchanger and all other hoses are hot to the touch, is this normal due to the hot coolant in the motor or is this definatly a partialy clogged exchanger. Thanks, Wes.