They are fully closed cooling systems, and yes I was referring the elbows after the
blocking plate that mixes the sea water back into the exhaust.
Are you talking about risers/spacers.... similar to this?
Depending on the elbow (ported or not ported), the plumbing and where the block-off plates/gaskets are located, these may be within the closed loop, or they may be within the seawater loop.
Those where replaced with new and hold at 80-90 degrees with temp gun. The boat is out so in going to take the advice and pull the water pump and either rebuild it with new cam or just replace with a new one
Which style seawater pump? Belt driven or crankshaft style?
and pull the heat exchanger and u-cooler off to have to better inspect and clean them.
As for the main heat exchanger, the seawater side of the tube bundle is fairly user friendly.
However, the ethylene glycol side of the tube bundle is not!
If the closed cooling systems were added to these engines, the H/Es may have a build up of rust scale within the E/G side of the tube bundle.
If so, this would hinder their ability to remove engine heat. Much like a car/truck radiator that needs to be rodded out and cleaned!
For peace of mind I will probably pull the water pump on the engine and replace.
FYI, for engines fitted with closed cooling systems, you can save a few dollars by using the automotive version engine coolant circulating pump.
The Circ Pump will not know that it's been installed on a Marine engine!
My motors sit outside under boxes on the back deck making it pretty ez to get at everything. I'm no expert by any means but it just seems like the problem could be in the closed side flow. The water flow out the exhaust is strong the elbow/riser temps seem normal but manifold temps where the coolant flows gets to hot. I'll post more when I get the chance to pull the parts off and inspect. Unfortunately I wont be able to verify anything for sure until spring ha
FYI again..... the coolant within the engine is thermostat controlled. The thermostat holds back coolant on an "on-demand" basis, and then releases it as required.
Without seeing a schematic of your cooling system, I would say that most exhaust manifolds receive coolant that is not thermostat controlled.