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Rough idle after overheat and impeller replacement

B

Bthomas

New member
Have 1989 mercruiser 3.0 with digital ignition. Was out on water and cruising along at about 3500 rpm. Was running good for about 15 min then started losing power. Noticed temp was in red. Not sure what temp as guage doesn't have degrees just lines. Sat anchored for about an hour to let cool down. Pulled water inlet hose off and noticed no water pumping in. Got a tow back to marina and tried to start just to get on to trailer. Was very hard to start and keep running just to get it out of water. Of course, the impeller had gone out. Replaced impeller, and housing. Back flushed hoses to be sure no remnants of bad impeller in system. Also while having lower unit off , i replaced the oil seal where drive shaft enters upper unit. Figure while in process , I cleaned spark arrested and installed new spark plugs. Got everything back together. Now it has a hard time starting. Have to give it a few pumps and hold at half down to get engine running. Once return to idle position, it shakes violently then dies. After about 5 min of playinh with throttle and get it a little warm, it will finally idle but it's at 800-900 rpm with a lot of shaking. Thought maybe one of the new plugs wasn't quite gapped right so I rechecked all. Choke looks to be opening and closing as it should. Before impeller failing and overheating ,engine purred smooth at the 600-700 rpm idle. It'll run smooth above 1000 rpm. Took it out and ran around lake for about 1-1/2 hrs. Runs great but when put into neutral and idle it'll start shaking and die in a few seconds. Have to give it about 3/4 throttle to get started again. Need help. As stated, engine ran great with no issues before impeller fail and overheating ..
 
FYI, Two seals for drive shaft in upper housing........The one you replaced is there to keep grease on the splines and free from water.

What may be your issue is a vacuum leak. My suggestion would be to start and get it to idle the best you can and use some Carb cleaner spray and spray around carb. See if idle picks up or slows down.

Unless you started to melt the rubber exhaust boots and heard the crackling of the hose clamps the you may have only got it hot but not actually over heated. But look for vacuum leaks first.
 
Yes, but didn't help much. When slowly backing adj. out it would get worse. Turning in slowly it would get a little better but rpm would raise also by about 100. Replaced water/fuel filter separator. Choke is working fine. Going to check compression most likely tomorrow. After talking with a mechanic friend. Suspecting it's gonna be a head gasket. Most likely between cyl 2&3. Praying that's all it could be and not any worse. Thanks for responding
 
Yeah know there's another seal in upper but the lower one was in good shape, just figured I'd go ahead replace with a new anyway while had lower unit off.
 
Did you ever resolve the issue. I am having similar issues with 2004 3.0 volvo pentadrive (GM). Almost seems like a timing chain issue.
 
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