Re: Merc 4.3 water in cylinders
...and then it started losing a bit of power like it was starving for fuel. Slowed down to idle, then back up to 3000, ran ok for a minute or two, then losing power again. Brought it down to idle again and it dies. Attempts to restart are unsuccessful as the cylinders are hydro locked. ... Got the boat home, pulled the plugs and found a significant amount water in most of the cylinders on both banks. ... Compression test shows all ok... There is no sign of any water in the oil.... Could an intake manifold leak of some sort put that much water into the cylinders? Would it affect all/most cylinders instead of just one or two? Any way to test without pulling the manifold?
Not at all familiar with your engine although I get the idea from reading the thread that it's a GM V8. Also not yet sufficiently familiar with boat engines vis-a-vis risers and flappers and all that. BUT, from what you've said, you should be able to rule some things out and maybe stumble on the source of your problem.
You said the compression checks out fine in all cylinders. That would tend to rule out a head gasket. Plus, as you've noted, you have the problem in both banks, so both head gaskets would have to blow at the same time.
And you know that ain't gonna happen.
So let's think about it a bit. You've got "a significant amount water in most of the cylinders on both banks." What's "a significant amount"? I have to assume it's a few ounces at least because you said it was "hydro locked." Can you give us an idea of how much water was in the cylinders?
The problem is in both banks and it exhibited when the engine was running.
I'm thinking you should look at all vacuum sources for some kind of water intrusion into the engine via that source. I'd focus on all vacuum lines into the engine. I cannot see how a leaky intake manifold gasket could be the problem since you'd need some source of water (if only condensation) at the point of the leak in order for that water to be sucked into the cylinders. You're not likely to find condensation anywhere near the intake manifold gasket(s) on an engine that's been running and thus pretty hot, even if run only a short time (which yours wasn't -- it sounds like it was well-warmed up).
You say you've ruled out water in the fuel, and I'd tend to think that any significant amount of water in the fuel would cause the engine to run very poorly and stall long before enough water could accumulate in the cylinders to hydrolock.
I suppose maybe some kind of fuel mix which would leave water behind as an afterburned product might be possible, but it would have to be something exotic and, frankly, I doubt there is any such thing. As you may know, some gasolines have a small amount of ethanol in them and maybe it could be possible for "too much" ethanol to get into the mix????
But I doubt it. And I doubt that's your problem.
Given how it happened, it sounds to me like maybe there's some vacuum line that's connected to some kind of boating gizmo which, when it goes dysfunctional, allows water to be sucked into the intake manifold via the line. Or maybe a vacuum line broke or came loose and went over the side or into the bilge and is sucking water into your engine.
I'd look at ALL the vacuum lines and check 'em all for signs of water in 'em.
Just trying to help. Like I said,
boat engines are not my thing -- yet. If I get mine into the water next summer, I might begin to get expert on the particulars of boats and boat engines. And I do think that kicker motor sounds like a good idea. Not exactly sure what that exactly is, but I think I've got an idea of what it's about. And I think I might just want one myself before I wander out too far from shore.
