Engine overheating at high rpm

[Wave Smasher]

In. March,2016 Dealer installed new mercury mercruiser remanned I/O package, 350/300 mpi Alpha SN 1G408350 complete with outdrive with(now) 550 hours in a 1986 sea ray 230srv.Constant issues AFTER 2nd year.2018,ECM REPLACED under warranty after Mercury ran dealer ragged with 14 visits over 3 months.2019 brought overheating above 3500 rpm,Dealer replaced lower unit water pump twice,t-stat twice,Engine water pump,installed clear hose looking for bubbles(none).Water flow is adequate.I can still use the boat,but must keep under 3500 rpm.The engine gets flushed with Salt remover every other outing.I need help resolving this as the warranty is over and starting to cost me lots.

 

[zealer]

Do any alarms go off or does it merely show high temp on the gauge? Is it raw water cooled or closed cooling?

 

[Wave Smasher]

Yes,Alarm goes off,raw water cooled

 

[alldodge]

Do you have the 3 or 7 point drain system?

An IR temp gun has been used to verify it is over heating?

 

[kenny nunez]

I was on the Donzi site recently and several members said that their overheating problems went away after they added a through hull suction to feed the engine pump along with the drive pump.
If you have the 7 point drain system remove the plastic housing on the port side of the engine and check that there is no restrictions in the bottom of it on the incoming side.
When I bought my Donzi I found 4 pieces of the engine pump impeller in that housing. I added the through hull fitting with good results.

 

[Wave Smasher]

7 point.I will check that and the power steering cooler.Just not as agile as I used to be,but,I'll get it done.As far as IR,YES I did.The t-stat area stayed at 140-164.The exhaust manifolds were hitting 200 +,The risers ,180 + on both sides.I took the 3/4 brass plugs off all fixtures,one at a time,front to back ,pumped water through.really good heavy flow from each section.This setup has been dealer maintained since day one.all scheduled maintenance done.I do about 200 hours a year.

 

[alldodge]

t-stat area stayed at 140-164
exhaust manifolds were hitting 200 +,The risers ,180 + on both sides

These are temps at or below 3500 rpm correct?

 

[kenny nunez]

The power steering cooler is a “straight thru” style. It is not the place that will get stopped up and the fuel cooler is the same style. Remove that plastic housing just next to the power steering pump and look in the bottom of it. There may be nothing in it but you still have to check.