350 Mag MPI Overheated....

[myers71]

Hey everone!

I have a '98 PRE2000WT with the Mercruiser 350 Mag MPI and 365hrs on the clock...Well, I lent it to a buddy last weekend and he returned it saying it kept stalling out on him.

Thinking it was a fuel problem (ethanol/water), I flushed the fuel and replaced the water separating filter. I took it out the lake she started up fine and was running smoothly.

I was watching the gauges and everything was looking normal and the temp gauge was reading about 150 deg when I started smelling something hot. I felt the exhaust manifolds and they were scortching hot!!! I then squeezed one of the coolant hoses and didn't feel much pressure so I immediately shut down the engine and loaded her back up on the trailer.

So ,I think I lucked out without any major damage (oil is good, she's was running smooth w/no odd noises), but I was wondering...Is there anything else I should check out? My buddy stated it stalled out on him 3 times and the temp gauge was reading around 200 deg. I wondering about exhaust damage etc. I think there are flappers in the manifolds to prevent water from entering the engine when slowing/stopping.

Anyone else have this happen? Lets hope I got lucky here!!

Thanks,

-Tim

[Shamus]

Why did it overheat? Impeller, thermostat? Mine did that once, alarms went off. Got really hot. I shut er down and paddled to shore. Changed the impeller and thermostat and it was good to go. I have the same motor, they are tough as nails. You would probably know it if you overheated it enough to do any damage. As long as you found the initial problem....

Your buddy seen that it was running at 200 degrees and let it shut down 3 times??!!! If that was my buddy he would get a kick in the N@#ts!!

[dogbert]

The engine will go into limp mode when you overheat. Don't worry, you probably didn't cause any damage. If you haven't changed the impeller in the last 2 years, it's time. If you did, you either sucked something up into it and shredded it or you sucked up something that's obstructing the water intake. In the case of the latter, just remove the intake hose before it goes into the transmission cooler.

[myers71]

Thanks for the responses! It helps ease my mind a little. The old girl is in the shop getting the raw water pump impeller replaced. It's been 2 years since I've replaced it and in fact, I had a spare one on board because I was planning on doing it this year! I'm waiting to hear from the shop if this was the culprit or if it was an obstruction.... I usually do it myself, but under the circumstances, I figured it would also be good if the rest of the boat was gone through by a professional as well.

Thanks again! As soon as I hear more, I'll post with the updates...

-Tim

[Joeprunc]

If the impeller was the culprit, I'd ask for the old impeller and any parts of it that they flush out. The reason behind this is if you impeller blows apart and the fins tear apart, all that rubber goes in your block. This is a check for you to see if they flush most of it out. I'd also keep an extra eye on the gauge for the next few times out. The rubber can also get stuck in the thermostat which may also be helping with the lack of pressure.

[myers71]

Yep, the impeller blew up! I stopped by as they had all of the hoses off, the trans cooler apart, and the thermostat housing off cleaning out any impeller debris they could find....

I have the old impeller, completely fin-less, and a baggie of as much impeller parts as they could fish out. Hopefully any parts that are left will wash themselves out.

So far so good for the test run. Water temps stayed nice and low and the engine was running like a dream as usual.

Thank god the engine safety sensors/computer did their job! I know if I was operating the boat and it stalled for no apparent reason, I'd be sure not to operate it until I knew what was wrong first...Not run it and watch it stall 3 more times...

Now, hopefully the buddy that borrowed it will be buying it, and not using this as an excuse to back out of the purchase. Besides he also trashed the cover.

After all...I need to make room for a new Tige for next spring!

[2whlin]

I just had impeller start to go but don't see where the pieces I found came from because the impeller does not show as much damage as pieces found??? So now I have to take the hoses out and the trans cooler apart? Where is that, guessing I follow the hose down flow??? Sucks cause family are at the lake and I'm headed back in the morning to put the impeller pulley/houseing assymbly back on but now worried about other debree that might have gone further down???