Overheated Mercruiser 3.0

[Denis O]

Back in May I had a small problem whereby the temp gauge was playing silly buggers and with the help of the kind folks on here I managed to change the stat and all was well again.

However, took her out yesterday, after 3 weeks on the mooring, and apart from a knackered battery (radio left on standby) I ended up with a major overheat. Left mooring and zipped round the corner to the gas station. About a mile. Filled to the brim and then heading out of the marina at 4 knot speed limit I was standing to the left of the helm and not looking at the instruments. Got to the end of the 4 knot limit so sat down to open her up and noticed the temp gauge was up at 240F. Immeditely switched off and the engine continued to run really rough for about 10 seconds (like a car that needs a decoke) and then stopped.

Got out of the main channel and dropped anchor and opened the engine compartment. There was a couple of mists of smoke and a lot of heat so we sat and let the engine cool to 180F. Then tried to start which it did so not siezed. Switched off after a couple of seconds and noticed small pieces of what I think is impeller out the back of the boat. Is it possible that it would spit out bits of broken impeller.

We waited for a tow back to the mooring and the boat comes out tomorrow to have a new impeller fitted.....if that's the cause.....which I'm guessing it is. This is our first year in the sea so I'm wondering if that will shorten the life of the impeller. Remember, it's already had a new stat.

Now the $64,000 question. What damage could the overheat do. On the assumption that the impeller was the root cause then that is easily and cheaply fixed. What else should I have the engineer check to make sure all is well when she goes back in the water.

 

[omega2]

Sounds like you caught it in time, the impellor should do the trick, If it were mine I would suck it and see. And yes the broken bits will get fired out the back, but a good idea to check the plumbing from the pump to the exhaust outlet, to make sure all is clear.

 

[tinkicker0]

You will also need to change the exhaust flapper valve as it will be toast.

 

[volvopaul]

If its on an alpha 1 leg the bits won't be impeller as the impeller is in the leg. More like bits of exhaust bellow.

I'd be looking at the leg Drop the bottom off to inspect the impeller. Run it with muffs first to check that you do have water even getting up to the engine .

 

[Denis O]

Thanks guys. Hopefully no major issues.

It's coming out of the water today and hopefully can get it looked at tomorrow.

 

[Denis O]

Update.
The boat was finally looked at on Monday and the impellor was found to be completely shagged, rubber spinning on the metal. The heat had also cooked the flapper valve and just the metal and grommets were left.

All changed and just waiting for a couple of gaskets and new grommets before putting it all back together and running her up at Xmas.

Looks like I've been very lucky and I'll make sure to keep my eyes on the dials in future.

 

[dpb]

A loud audible warning should have sounded before the overheat got critical, the same sound you get when you first turn the ignition on...might be worth checking that out for the future.

 

[Denis O]

A loud audible warning should have sounded before the overheat got critical, the same sound you get when you first turn the ignition on...might be worth checking that out for the future.

I did wonder about that and thought it strange that I hadn't heard any warning. I do get the sound when I first switch the ignition on and it's not that loud so perhaps I missed it. I'll get the engineer to check it's working when he puts it back together.