Optimax 115 Overheat

[JesusOffline]

Hey everyone,
i have a 1.5L Mercury Optimax on my boat which has a very weird overheat. I have replaced the impeller, its housing (slightly scored top and bottom), the tube gasket going up to the copper tube which was shot, thermostat, poppet valve, cleaned the compressor strainer, new belt at the top, etc.

Now, after all i have changed, it still overheats, when the new impeller was placed the tell tale went twice as far, however when i take it out to the water it takes like an hour or so of sailing (above 3-4k rpm) to overheat. When it does overheat, as long as i keep it under like 1700 rpms, it takes me back home with the tell tale being relatively hot. after an overheat i took off the cover and saw that the hottest component was the pulley of the compressor, where the sensor goes on the compressor head was cold, and the block was sort of hot, so im not too sure what the issue could be.

Any help is greatly apreciated, appart from maybe a blown air compressor head gasket as the water looked whiteish with soda bubbles at 2k+ rpm, im not too sure what else the issue could be.

Thanks to everyone for their time.

 

[Chris1956]

Check your head bolts for proper torque. If they are loose, exhaust gasses can leak into the cooling jacket and cause overheat.

 

[JesusOffline]

Check your head bolts for proper torque. If they are loose, exhaust gasses can leak into the cooling jacket and cause overheat.

compression is good though, 115 psi, inside the range for these 2 stroke optimax engines.

 

[Texasmark]

compression is good though, 115 psi, inside the range for these 2 stroke optimax engines.

For smaller engines like the triple and 4 cylinder 2 stroke loopers in the 90-125 HP class, the service manual states that if compression is below 120 PSI, expect problems.

 

[JesusOffline]

For smaller engines like the triple and 4 cylinder 2 stroke loopers in the 90-125 HP class, the service manual states that if compression is below 120 PSI, expect problems.

i guess that could be right but this is from the optimax 115 manual