I Can't Fish Because My Motor Won't Run Right

[djriptide]

I have a Mercury Optimax 75 horse, 2006 that I bought new 12 years ago. The motor has started giving me a steady overheat beep above around 2200 rpm. Had mechanic out and impeller, housing etc. has been put in new. New thermostat installed, compression checked, all three sensors are good, telltale good, battery fully charged and new. Looked inside when the thermostat cover was off and the motor looks very clean. Motor ran great on muffs at 4000 rpm for several minutes while the mechanic was here. Took the motor out on the water and ran it up to 4500 rpm for around 2 minutes and Guardian shut me down. Had to limp in at 2000 rpm. On the way in I took cover off the motor and ran at different rpms until Guardian shut me down again. Each time I put my fingers on the thermostat cover and I could hold them there all day so not overheating. Mechanic coming back next week but It's costing me more and more and I'm retired. Any help would be appreciated.

 

[Scott Danforth]

Salt water or fresh water?

Guardian is more than temp, its also oil level, water in fuel and a few more systems

 

[Chris1956]

Do those Optimax's have an overheat sensor on the compressor as well?

 

[djriptide]

Salt water or fresh water?

Guardian is more than temp, its also oil level, water in fuel and a few more systems

Yes, according to the computer oil sensor is working fine. Oil is being used and I'm in salt water. There's no water in fuel and as I said ran fine on the muffs. All sensors read fine on the computer.

 

[djriptide]

Do those Optimax's have an overheat sensor on the compressor as well?

Yes, it does have one on the compressor and we've swapped sensors around on the engine to make sure all are working. Compression by the way is fine.

 

[Scott Danforth]

Being in salt water i would assume you have a lot of deposits in the motor and you may be overheating

 

[djriptide]

Being in salt water i would assume you have a lot of deposits in the motor and you may be overheating

Not overheating, as I said I can hold my fingers on the thermostat cover and leave them there. Tested temp while on muffs running at 4000 rpm for several minutes. Temp on computer was 102 degrees. Looking inside the thermostat cover all looks exceptionally clean because I've flushed my motor every time I fished without fail. The boat is never left in the water.