Boomerang Searay 1999 240 Sundancer,5.0...

[jaclor]

Boomerang

   Searay 1999 240 Sundancer,5.0 Mercruiser2 bbl. Alpha 1

Port bank on engine overheating at over 3000 rpm.Suspected head gasket so pulled head ,checked for cracks,valve job,seals,new head gasket and tty head bolts.Compression good.New water pump impeller and engine water pump.New temp sender and thermostat. This is a raw water,open cooling system on the great lakes.Never in salt water.Still overheating persists. Any ideas would be appreciated.

[SMT]

Recheck temp sensor. You could have a bad one or it is not the proper sensor. They have different ranges.

[twin_engine]

If you have power steering, check the water cooler leading to it. I had a similar problem and after exhausting everything else, I found the cooler had an obstruction, so water was not circulating as readily through the whole system. To add to the problem, it had a cooler coming off each engine, one did not even connect to anything, except being in the cooling loop.

[jaclor]

jaclor; many thanks for the ideas. Checked the water circulation form the stern drive thru the power steering cooler and found it acceptable. 6 qts in 15 sec. with no bubbles. (at 1000 rpm). pulled plugs and found 6 &8 dark and carbon covered. Over heating persists. To check compression again but suspect head gasket. Thanks again for the comments and will post final results when boat is hauled out and addressed next month.

[mike_v_]

Have you tried replacing the thermostat?

[PeterG1]

I agree on the possibility of the bad thermos tat, also did you have the head magnafluxed?

[jaclor]

I’ve taken the head off thinking it was a head gasket. Shop stated it is a cracked head. Hopefully this will resolve the issue of overheating.
Thanks everyone for the suggestions. Will let you what happens when it’s all back together.