Need help solving over heating problem

[Mike Davis]

My cd 31 is overheating. After launching boat, a few minutes later I had to shut engine, which is a Universal M25. The following was done afterwards.
* checked impeller.
*seawater is spitting nicely
*changed freshwater pump
*burped thermostat housing petcock
*changed thermostat and gasket
*removed heat exchanger and had it flushed out under pressure
The mixing elbow was changed 2 years ago. Last year, there was zero problems with engine.
I start the engine, it runs well for 5 minutes. I go down ladder and put my foot at the water exiting the exhaust and it is cold. I'm sure there is no antifreeze circulating, but I'm not sure what to do to make it circulate, since I changed water pump. I believe there is air in the fresh water circulating system, but am not sure how to solve the problem. I appreciate your input. Thank you,
Mike Davis

[Paul D.]

Before doing anything massive, I suggest putting an infrared surface temperature thermometer on the motor just to be sure it is overheating and not a sensor. Just to be sure. Good luck!

[Mike Davis]

Question on exhaust: Is the water coming out of the exhaust supposed to be warm? I think so because the heat is "exchanged" in the heat exchanger, but I'm not sure. Thanks

[riveredge]

I had a very similar problem and think I solved it last week. Trying to solve a chronic hot running problem I replaced everything in the raw water system except the hose going from the raw water pump to the heat exchanger. When I finally removed that hose it was clogged with mineral deposits and small crud. Anyway my advice is check all hoses even if it seems illogical that any one would be blocked. The last one I suspected of having a problem was the culprit.

[Mike Davis]

The problem was solved today. After heating up the engine, I took off the nipple on top of the thermostat and let the air out. had to do this several times until there were no bubbles. I also revved up the engine a few times. Maybe this cause more pressure buildup, Im not sure though. After the engine ran for about 15 minutes, I walked down the swim ladder and stuck my foot near the exhaust. The water coming out was warmer than yesterday. I then felt the heat exchanger and it was warm. Now I can start the season. Thanks for your input.
Mike