Broke Impeller, Overheated, now Water Intrusion

First....my outboard is a 1988 Mercury Inline 6 "Tower of Power" - 115 hp

After pulling a tube at 4500 rpm WOT for about 10 minutes, my engine acted like it was running out of gas and stumbled back to 2000 RPM for a few seconds before resuming at 4000 rpm. I pulled back the throttle to idle speed and checked the motor and saw that it was not "peeing". I immediately shut down the motor. I assume that the water impeller has failed since it no longer shoots water out the pee hole.

After being towed back to the marina, I checked compression and found the cylinders 1-5 have between 110-117 psi...however, cylinder #6 has ZERO pressure. It also shows a clean spark plug and it seems to have water droplets on the spark plug.

It is possible that #6 had slight water intrusion before this incident because #6 also looked "clean" a few months ago when I changed the plugs.....but at least then it have over 100 psi.....perhaps this episode made a moderate problem much worse.

I assume that a rebuild is in my future .....how bad is this and how much is it likely to cost to pay someone to fix it? Although I have some mechanical ability, I think this issue is probably over my head.

Re: Broke Impeller, Overheated, now Water Intrusion

Hi,

Sounds like a rebuild is in your future. Usually No 1 or 3 would have no compression. No 6 makes me think your exhaust port cooling gasket is bad.
This causes water to get pulled into the cylinders turning to steam super heating your piston. Not a good thing.
Good luck.

Re: Broke Impeller, Overheated, now Water Intrusion

-ouch-

You may have overheated but noticed in time not to suffer permanent damage to upper cylinders. Pistons may have grown due to heat and started to drag on the skirts. Condition of the impeller? If it looks okay, you may have exhuast in your water passages blocking water flow.

#6 is likely pulling water in through lower crank seals. Still plausible you have cracked an inner water/exhaust baffle. Needs investigation.

Zero compression is not a good sign at all obviously.

Pull the intake covers off the starboard side behind the electronics and inspect the cylinder/piston/rings for damage.

Re: Broke Impeller, Overheated, now Water Intrusion

Thanks for the replies.....

What is a fair price to rebuild the powerhead of a 1988 Merc Inline Six?

Re: Broke Impeller, Overheated, now Water Intrusion

Hi,

That is hard to say. I would get your local shops labor rates and ask if they
charge Merc flat rate or real shop time on a rebuild. If a shop charges real time make sure you find out what the flat rate time for comparison on the final bill.