Cooling Issue Crusader 454 XL

[390Express]

Apologies for the duplicate post, posted in gen maintenance, probably better suited here:

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?

[km1125]

If it was OK before the valve work, then I would not suspect bad parts (at least no initially). You need to get all that air out of the system. A couple warm up cycles might be necessary and purging the air in between.

If you're still getting air, then I'd suspect you might have a head gasket leak into the cooling system. If you have something capable of doing a pressure test, you could do that on the closed system to make sure you don't have anything leaking.

[390Express]

QR_BBPOST If it was OK before the valve work, then I would not suspect bad parts (at least no initially). You need to get all that air out of the system. A couple warm up cycles might be necessary and purging the air in between.

If you're still getting air, then I'd suspect you might have a head gasket leak into the cooling system. If you have something capable of doing a pressure test, you could do that on the closed system to make sure you don't have anything leaking.

Took 5 heat cycles (and 2.2 gallons of coolant) to bleed all of the air out, but it finally worked itself back to good. What a pain.

[Viper]

Glad you got it figured out.