Overheat alarm at WOT

[TSanders13]

I have a '96 40 Mercury 4cyl. When running at full throttle for a minute or two the overheat alarm sounds. Just under wide open the alarm never sounds. If I back off on the throttle after the alarm sounds, it stops beeping after 30 sec to a minute. Getting 10 lbs water pressure, new water pump.

 

[TSanders13]

Re: Overheat alarm at WOT

^

 

[mcgurk34]

Re: Overheat alarm at WOT

I had the same problem, with my 1989 50 HP 3 cyc mariner, that had me stumped for two years. I replaced the water pump twice. I opened the covers on the engine and the water passages were clean, T-stat was removed etc. Nothing worked.<br />This spring I noticed that the engine was mounted two inches high on the transom. The cavitation plate was 2" above the bottom of the hull. I lower the engine two inches and problem was solved. At WOT, on plane, the engine must have risen out of the water enough to suck in air causing the alarm.

 

[TSanders13]

Re: Overheat alarm at WOT

Thanks, I'll give it a try. The motor is on a jack plate so this could very well be the problem.