Cooling System Issue (454 XL)

[390Express]

Boat is a 1996 390 Express, complete closed cooling, only thing cooled by the raw water pump is the risers and heat exchanger.

Issue: Boat is running hot on the engine circulation pump side. New thermostat, admittedly some air in the system. Boat was apart for recent valve job, did not run hot prior.

After about 5 minutes of run time the manifolds are about twice as hot as the port engine that runs properly. (Port engine manifolds are around 87 degrees, the starboard engine with the issue are around 150 degrees. Shortly thereafter the entire system heats up, and eventually overheats.

The boat does not have a cap on the heat exchanger. The highest point is the radiator cap on the thermostat housing, but there is so much flow through the housing (there is something like 5 lines connecting at that point), I can't run the boat with the cap off. I just got about a gallon and a half worth of air out of the system (replaced it with antifreeze). I'm hoping it's finally good, I have to try to run it again. I have ran it with the bleeder bolt off, until coolant came out of the heat exchanger. Is there anything else I can be doing, or anything else I can check in the meantime?

There's really only two components to the system - the heat exchanger and the circulation pump. Is there a good way to tell if one or the other is bad? Or should I just keep bleeding air out and hoping for the best?

[jcoll]

"Boat was apart for recent valve job, did not run hot prior." This statement leads me to believe that air is the culprit. The only thing that changed was the amount of air in the system so it should run normally once all the air is out. I've experienced some difficulty trying to bleed the systems myself and it did take a while to get all the air out.

I did forget about the possibility of a head gasket installation problem as someone mentioned.