Last year, one of my BBC motors was getting getting water in the oil. With new oil, after 30 minutes of driving, the oil looked like a milkshake. We looked at the plugs to see if any water or rust visible, but they looked good. Next thought was the intake manifold. We pulled it off, saw a few suspect areas put a new gasket and oil in, but same problem.

Next we thought maybe the Stellings headers were leaking. We pressure tested them, but couldn't find anything more than a tiny drip every so often. We thought maybe the headers were heating up and leaking, so we sent them to a shop in Miami that originally built the boat. They checked them out and said they seemed OK.

So now I decided to just the motor, take it apart and see what the problem was. I get the block apart, and see that the previous owner had welded the crank and that when it let go, it damaged some pistons including one which had a cracked wrist pin hole. I was amazed that the engine held together like that in the 3 years that I owned it.

The heads were old and the block had some corrosion and stains that didn't clear up on honing, so we decided to just scrap the whole thing except for the headers, carb, valve covers, oil pan and oil cooler heat exchanger. The new motor has a new crank, rods, pistons, block, heads, intake manifold, rockers, flywheel, etc.

So the new motor goes in, we go out for 1/2 hour, and the same thing - milkshake oil. Unless something is wrong internally with the new motor, which I really doubt, it would seem logical that it is the headers or oil cooler heat exchanger. I wouldn't think that it would be the oil coolers because the engine oil pressure is 50 - 80 PSI. I would think that if the oil cooler had a leak, I would see oil in the water, not water in the oil.

Is there a point where the oil pump could be sucking in water? Anybody have some ideas? I am guessing that the oil coolers are the culprit though I don't understand how.

I am having the same problem with my 7.4 MPI Merc. Was told to check the outter 4 corner intake manifold bolts, I will, but I doubt it. Doesnt sound like your problem either cause you just redid your motor. I was really hoping that it was just my cooler. I cant really see how if it were cracked or worn somewhere that you could only have milky oil in the crank case withouth the rainbow colored water coming out of your exhaust due to oil contamination. This motor has been pushing me up and down the east coast since 99 cooled on raw salt water. Gets a flush after every use and I have always kept up on oil changes... she has almost 1500 hours on her so I should say she does not owe me a penny. Thought I could go for another year or two of light use but I may be doomed!

Let me know if you hear of any other possibilities.

Rush, take oil cooler off. if still milkshake, that isn't problem. Plaineman, 1500 hours of salt, block or heads corroded through. probably the heads.

I just did heads, manifolds and risers two years ago... I am going to try run it for a while on the water and see what happens.

Thanks

We had one that did the same thing. Turned out the inner wall of the rubber exhaust hose had split. When you started the engine it came down like a flap and forced water back into the cylinders, was worst when the engine was run then turned off. Never did hydro lock, but milked up the oil.

Inner wall rubber exhaust? The only rubber hose I know of on the exhaust is the water feed for the water jacket headers and a rubber connecting joint that seals between the end of the header and the exhaust extension through the transom.

I, would pressure check the oil coolers, first. Even though the oil pressure greater than the water pressure, it still mixes. To back up your whole build, you should always pressure test oil cooler and your exhaust. One little leak in a header can ruin your day, left un-noticed. You could have a small leak in a head or even your block if not inspected or tested at time of rebuild. You can make block off plate to pressure test your engine complete.

My nickel is on the oil cooler, when running the drive pressure can overcome the system pressure and force water into the oil, with a good tight system this can happen at speeds above 30 mph.

I ordered new engine oil and transmission oil coolers. I am out of town this weekend, but hope to test on July 4th. I hope it is one of the coolers though it still seems strange. When I am running, oil PSI is between 60 and 80 PSI. I thought water pressure was much lower than that. Not really anything left other than the headers and coolers unless the engine builder screwed up - and I doubt that because he has done lots of motors for me, and this is the same problem with a new motor but old coolers and headers.

Looks like the source of the water leak was the coolers. Took the boat out last weekend and oil still looks good. Water PSI was about 12 while engine oil was 60-80 PSI. I wouldn't think a leak would result in water going into the oil, but looks like it happened. Maybe it leaked when the engine was off? Anyhow, glad to have problem gone.