Join Date: Aug 2011
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It is very likely that there is some air in the freshwater side of the cooling system. The temperature you saw is probably an elevated temperature of the air. The engine was probably hot but not as hot as indicated.
To get the air out, try the following:
1. Make sure the coolant cap is on and closed and the air bleed valve is closed
2. Start the engine, run until thermostat is open. You can tell the thermostat is open when the temp gauge registers above zero
3. Rev the throttle between idle and operating RPM (approx. 80% max). Do this back and forth slowly. This helps work the air through the system to the manifold where it will rise to the top. Keep an eye on the overflow container and fill it with more if needed as antifreeze/mix replaces air in the loop. If the engine gets hot, shut it down and repeat once cool.
3. Repeat process until temp holds steady. Probably will take 4-5 rounds
After some routine heat exchanger maintenance (removed, cleaned, etc.) my M-18 was heating up. The bleeding and coolant cap techniques weren't working very well. Another person at my marina with an M-25 recommended the approach above and it worked like a charm. It's a technique not mentioned in any of the texts/books.
If that doesn't work:
1. Check hoses, clamps, coolant cap, and bleed valve for leaks that might allow air
2. Check you heat exchanger for sufficient flow
I've read that many people upgrade the M-25 heat exchanger with a 3" model instead of the 2"