Mariner 50 overheats at high RPM

[McGurk]

My 1986 Mariner 50, 3 cylinder, sounds the temperture alarm (Steady Buzzer)whenever operating the boat at high speed. The alarm goes off as soon as I back off the RPMs to mid range or idle. Good water flow from the telltale at all RPMs. Rebuilt the water pump and electrically tested the temp sensor in boiling water. Open circuit at 212 degrees, closed circuit above 240 degrees. No thermostat on this engine design that I can see. Next step??

 

[johnmoeller]

Re: Mariner 50 overheats at high RPM

Seems you and I have the same problem. Iv'e lookd at everything as well. A mechanic said to look for ariated water, ie. . a intake problem allowing air to intrude into the pump.

 

[BillP]

Re: Mariner 50 overheats at high RPM

Pull off a head and see what the water passages look like. They may be plugged up.