3.0 exhaust manifold over heats

[Lou C]

https://www.marineengine.com/parts/omc-parts/omc-boat-parts.php?year=1998&hp=3.0&model=302CMBYC&manufacturer=OMC+stern+drive&section=Cooling+%26amp%3B+Oiling

OK this is a diagram for a 1998 OMC Cobra 3.0 but keep in mind this is the joint venture period when OMCs and Volvos were basically the same. So there is no bypass to the exhaust pipe here and I think the exhaust manifold and elbow get a constant flow of cooling water. If the OP can convert his engine to this system and use a 160 stat, it may solve the problems. I am still surprised that Volvo designed it that way with no bypass of cool water to the exhaust elbow which is always the hottest part of the system. If the 'stat doesn't open fast enough, that will cause a very rapid increase in temp with the manifold right up against the side of the cylinder head, all that heat gets transferred to the cyl head.
So the OP might have to source a different 'stat housing and block off that port for the bypass on the exhaust pipe to prevent water leaks. Not sure if it would work, but what do others think?

 

[ESGWheel]

That would actually "bypass" the elbow and the water goes straight into the exhaust pipe!

Ah, I see. You are right of course! I was looking only for water downstream of the manifold and saw that. No coffee yet is my humble but not worthy excuse. :-(

 

[ESGWheel]

oops...