4.3L water in all 3 port cylinders

[the man]

Re: 4.3L water in all 3 port cylinders

yeah- i found the diagram on a local supplier website. so, with these failing once, what is to keep them from failing again? maybe the design is not as flawed as my first reaction may have indicated, but depending on a little flapper valve, that can obviously fail, seems a bit ridiculous. just my opinion; not much i can do about it. it seems like taller risers might have been a good idea, or some kind of redundancy.

anyway, problem found for others with the same symptoms.

 

[TilliamWe]

Re: 4.3L water in all 3 port cylinders

The reason flappers fail is that when an impeller fails to pump cooling water, the hottest thing is the uncooled exhaust exiting the exhaust manifolds. This melts the rubber flappers. So if you never ruin an impeller, you don't ruin flappers. Not a design flaw, just lack of maintenance.

 

[the man]

Re: 4.3L water in all 3 port cylinders

The reason flappers fail is that when an impeller fails to pump cooling water, the hottest thing is the uncooled exhaust exiting the exhaust manifolds. This melts the rubber flappers. So if you never ruin an impeller, you don't ruin flappers. Not a design flaw, just lack of maintenance.

just a note for others with same experience and/or symptoms. The above quote is likely very true, although not by intention or neglect. This started with me paying a "mobile boat mechanic" (aka hacker) to change my impeller as a preventative maintenance move. This was installed wrong (not sure how) and the impeller i later found to be stripped on the shaft contact area. when the boat overheated, although i caught it immediately, i must have fried the flappers. not being experienced, and looking in the exhaust manual for the flappers location, i did not go straight to the problem. silly me, i should have known that the flappers are diagrammed not in the exhaust manual, but in the engine manual. who would think that they would be in the exhaust manual, being halfway down the exhaust system??? anyway, so i wore out the exhaust manual looking for flappers, never found them, and looked for the problem elsewhere. when it happened again, (water in cylinders) i think that this time is has caused damage to the point that the engine will not start.

so the moral here is this- it think: even though you think you know engines, and boats, and have over 40 years experience with both, you will learn something new every time. early in this process, i was advised that the problem might be the flappers; i couldn't find them, not looking in the right manual, so i ***-u-me-d that the issue did not apply to me. looking back, it is obvious what happened. although i had the best intentions, thought i was doing everything right, paid to have impeller replaced BEFORE it failed, spent hours researching and trying to learn- i still have an engine that appears to now be toast.

now- off to shop for outboards. keep the car engines on land.

 

[IdahoDoug]

Re: 4.3L water in all 3 port cylinders

That's a great followup post to update us. Much appreciated and it took you some time to discover and to post though you will benefit not a whit. Thank you. Also along these lines "reversion" was mentioned a few posts up which happened to me. An impeller went while I was warming the boat in the slip at 1800rpms. Temp alarm went off and I instantly turned the key off as it was closer than the throttle. Reversion (brief pressure wave in the risers) caused water to enter the cylinders through the exhaust valves. I was lucky in that I noted a funny hesitation when I engaged the starter and let go of the key instantly. Did some internet searches right from the slip, discovered that's what happens when you shut off the 7.4 at higher rpms. Pulled the plugs, turned over the engine to get the water out, got a new impeller in within hours and ran the engine to totally dry the cylinders. Hundreds of hours later the engine doesn't use a drop of oil so I was lucky.

Just wanted to mention this as I often see people on the ramp start the engine with the stern settled deeply, front on the trailer, rev the **** out of it to warm it and shut it off at high rpm. Worst possible thing you can do on many fronts. So only shut down at a dead idle or you risk water inversion into the cylinders.

DougM