Overheated engine bad.

[Truchero]

I have a fresh water system. I’ll first give a little context to my idiocy. I launched the boat for the first time on Sunday and it has been sitting at dock for a few days. I closed the raw water valve when I left. I came back with my father and was exited to show him how well it ran. Turned it on, checked the exhaust for water and saw water come out (it had some in the piping). I never opened the raw water valve . I then started to fool around with the shifter linkage inside the locker compartment. By then 10 min had passed. The temp was well over 200 and something and the coolant was about to pop the lid off. Obviously turned off the engine! I haven’t attempted to start it since.

I have to move the boat in two days. Do you think I’ve done permanent damage? What should I look for before attempting to restart it this afternoon?

Thank you!

[ndutton]

Replace the raw water pump impeller for sure. Beyond that, a successful cooling system pressure test would be reassuring as well as an exhaust system inspection for a damaged waterlift (if fitted) and damaged exhaust hose.

If you weren't too much over 200° you're probably Okay. As a benchmark, the alarm system available from MMI has a roughly 240° trip point.

[Truchero]

Thank you Ndutton, I'll pull the raw water impeller for sure and inspect the exhaust system. Unfortunately, I was way over 200°, again the coolant was boiling. Hopefully I haven't damaged anything permanently.

Anyhow, I have a very weird engine setup, it's a mix of the new and old version engine. I've researched how to do a cooling pressure test, but I'm confused about where to hook up the pressure gauge. You can see a picture of my setup in this thread. I know, I know, it has a lot of clamps! hehe.

https://www.moyermarineforum.com/forums/showthread.php?t=11860

Thank you again!

[ronstory]

A formal pressure test is always good, but if you don't see water in the oil or oil in the radiator or coolant leaking out, your engine will likely be fine. Actually, 10 mins of running without cooling raw water, likely the engine just did it's own "pressure" test.

I would go with Neil's advice and just replace the impeller and then run the motor at the dock until it comes up to temperature. If all looks good, go for a short motor-cruise and make sure all it good before venturing farther out.

[Mo]

I concur with both reply posts. Have a good look at your impeller and ensure it is all there. The ends may be worn down from the rotation without water. In such a case just replace it. However, if there is a piece missing that will have to be located and removed.

[scratchee]

I had an extremely idiotic overheating episode a few years ago. I was saved by a transparent plastic inline filter that probably shouldn't even have been in the cooling circuit. That filter ruptured when the coolant got too hot, forcing me to shut down the engine.

Anyway, after some troubleshooting and minor maintenance--nothing catastrophic--my engine is running better than ever. So it's entirely possible you have no serious damage.