Chevy 350 - Water in Oil

douglee25

Well-Known Member
Jan 13, 2008
4,744
Dallas, TX
Boat Info
Cruisers 3575
Engines
Twin 7.4l
My buddy has water in his oil on a chevy 350. I checked the
dipstick and it's painfully obvious. He just picked this boat up, so previous
work by the owner is suspect.

Let me know if my thought process is
correct for diagnosis -

Causes for water in oil -


1. Leaking riser joints
2. Leaking intake manifold gasket
3. Leaking head gasket
4. Oil cooler that is mixing due to a leak internally.
5. Cracked head/block

Here's what I would do...

1. Pull the plugs and turn the engine over with the key. Do you see water shoot out? Is it the center cylinders? If so, it's probably the riser gaskets.

2. Pull the risers and look at the surfaces. Do they look flat? No material missing or eroded on the mating surfaces? Do you see any rust traces down the manifold internally? If so, again the riser gasket may be leaking.

3. Pull the valve covers. Any milky fluid in the top end? Could be intake manifold gaskets.

4. He said compression numbers were all even? 170ish? That could be a sign that the head gasket is good, but a leak down test would be better (pressurizing the cooling end of the block). Sometimes this doesn't even show a bad gasket because the
block needs to be hot.

5. Pressure test the oil cooler.



That was my recommendation. Am I missing anything? If the oil cooler is good and holding pressure, would you throw new riser gaskets and intake manfold gaskets on and water test the boat? If that doesn't fix it, then I'd assume the head gasket must be bad or the head is cracked? Pull the heads then, get them manufluxed unless you can visibly see a bad gasket, replace the gasket, and finally water test again?


Doug
 

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