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Gents, While running the engine using muffs for cooling with the out drive on, or sticking a hose directly in the bell housing with the out drive off; can you force too much water into the engine and force water past the risers and into the exhaust manifolds? I removed my risers and manifolds and found them almost completely plugged with rust and scale . Since I was using a hose to cool the engine with these clogged manifolds and risers, could water have gotten into the cylinders and then down to the oil pan? I now have water in the oil and am trying to figure out how it got there. I have a 1990 MerCruiser 305 with raw water cooling. I guess what I'm asking is if your risers and exhaust manifolds are seriously plugged up and you are force feeding water from a hose into your engine, can that water wind up where it is not supposed to be? thanks for your advice.

If things were as plugged up as you said they were, anything is possible. I'd try a quick oil change with cheap oil. Run it to temp, and then change again. You'll see the dreaded milky color in the oil if you have other issues right away.

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2001 Horizon 260 - 7.4 Volvo GSI DP

It would seem to me that if your risers have that much rust and are plugged up -- there is also probably of rust at the mainfold to riser joint. That will cause water to be in the cylinders, and could lead to lots of issues. If you have enough corrosion that water is getting into the valley at the intake manifold, (assuming a V type engine V6 or V8) then that water will go right to the oil pan

I have never heard of high water pressure directly causing water in the oil pan, however if you have corrosion issues that could lead to lots of things.

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DaleG -- West Palm Beach FL
2003 240Horizon -- 5.7Gi -Duoprop

No if the water pressure was too high, the excess water would escape between the muffs and the drive or just blow through the risers and out the exaust. If you're getting water in the oil, it is likely one of the following:

1. rust eaten or cracked riser
2. rust eaten or cracked manifold
3. bad seal between intake manifold and heads
4. cracked block.

Don't worry, chances are, it's only the risers and or exaust manifolds. A simple test:

1. Change oil with cheap oil and filter.
2. Run on muffs.
3. Shutoff motor and check for water in oil or rise in oil level (because the oil will be on top of the water in the pan).
4. remove all spark plugs and see if water pours out of any of the cylinders.
5. Flip-flop the manifolds/risers (use the port side on starbord and vice versa). To do this, you will have to move some plugs and hose fittings around.
6. Change the oil (you can reuse the filter, but empty it of the contaminated oil), put spark plugs back in and run it again on muffs for a few minutes.
7. Shut it off, check to see that water is in the oil again.
8. Remove the sparkplugs and I'll bet you'll find that this time water pours out of the opposite side of the motor. Which ever cylinder bank you find water in will be the side that has a bad manifold/riser.

Now you're probably not going to replace just one riser or one manifold, because chances are the corrosion is just about the same in both. So you can save yourself a ton of time and just replace both exaust manifolds and risers and enjoy your boat another 5 years without worrying about them. Also, whenever you run it with water in the oil you're removing years from the end of your engine's life.

And if water sits on top of the cylinders it will hydrolock the motor which can lead to bent valves, broken starter or flywheel or worse.

Good Luck... Let me know how it turns out.