Omc loss of power and rpm

1990 sea swirl striper with a 4.3 liter FWC v6 and a omc cobra outdrive,ok lets start this off from what all i know that has happen, this winter we found alot of water in the oil...... after changing the oil we have run this engine hooked to a hose alot but have not found any more water in the oil. we took it out last weekend and it ran ok but on our return in from a bottom fishing trip we had a overheat that actually made the moter sputter and die..... after it cooled off a bit it would run at low rpms without overheating (enough to get us back to the dock and on the trailer. ) we found impeller worn and impeller case had gotton hott. these parts was all replaced. once again we took her for a cruise down the bay,, idles ok low rpms are good and pour the fuel to her and i can not build rpm enough to even get her on the pad. on a running look at motor we find alot of blow by coming from both valve covers and no power ....... worn rings? heads? help?

Re: Omc loss of power and rpm

I suspect that this engine ran hotter than you thought last year and an over heat on a 4.3 often times warps cylinder heads such that you lost head gaskets, accounting for the water in the crankcase last fall. Running on the hose never placed enough load on the headgaskets, you will not notice your problem until you put the boat into the water and put it to work.

Start testing, first compression followed by a cylinder leak down test to verify the head gasket leak. It may be quicker to go straight to the leak down test.

Once the heads come off, check them for straightness then send them to the machine shop for surfacing.

Reinstall with quality gaskets and NEW headbolts.

While the heads are off fish out all the old water pump impeller vanes out of the block so as to prevent their blocking the cooling holes in your new headgaskets, creating new hot spots/warping on your freshly surfaced heads. Also check the inlet side of the oil cooler for blockage by impeller pieces.

Also check exhaust riser water exit holes for impeller pieces blocking flow.

Re: Omc loss of power and rpm

This is why we HIGHLY recommend that impellers be changed AT LEAST every other year.

An impeller is a LOT cheaper then even a relatively minor overheat.

You are still getting off very lucky, this time.

Don't bet on it again, you can lose BIG.

Re: Omc loss of power and rpm

compression check on engine: 1,3,5 150 psi +
2 (ZERO) plus spark plug is toast! 4 150psi+ 6 165-180psi
still think its just the heads? i'll pull them tomorrow if your thinking this! thank you for your help........and yes wife already put the impeller change in the books for off maint.