1996 SN 5.7 water in oil

[StagNW]

1996 SN 5.7L ProSki PCM 290 hrs

I bought this boat, my first, Aug 2017. I did an oil change after putting about 20 hours on it. Seller had just changed it. When I pulled the cap off the drain hose, about 1/8 cup of water came out before the oil started draining. “That doesn’t belong there.” Other then that, the oil was normal. The inside of the valve covers looked normal.

I changed the oil before winter and kept it in my heated garage all winter. Ran the boat 30 hours this last year checking the oil regularly and each time the oil on the stick was full, clean and lacking odor.

Today I serviced the boat before hibernation. Before I did, I checked the oil on the dipstick, full, clean and lacking odor. Good. When i pullled the drain hose cap, the oil was laced with a yellow streak indicating, based on my experience, water in the oil. It wasn’t completely milky however it left a significant lace streak while draining. See photos.




So, i went up and pulled the oil cap on the valve cover and the little puddles on top of the heads and rockers is milky.



I had other projects planned for winter but i suppose this one will move up the list. -_-

Anyone have experience diagnosing this? I’m assuming Head gaskets or a cracked block / cylinder. I should have the tools to diagnose, not much experience with fresh water cooling systems.

Thanks in advance.

[Nautiquehunter]

GM had intake manifold gasket issues in the 90s . If its aluminum start there look at the gaskets in the corners where the coolant flows across . It will be obvious if that is the problem.

[StagNW]

GM had intake manifold gasket issues in the 90s . If its aluminum start there look at the gaskets in the corners where the coolant flows across . It will be obvious if that is the problem.

Well that’s good news, do you think there are any tests I should do before i pull the intake manifold if it’s aluminum.

[Nautiquehunter]

Its ether Intake heads or block . I would pull the intake and inspect the gaskets in all four corners .

[StagNW]

I pulled the intake, unfortunately the gaskets looked to be in really good condition. There was quite a build up of thick milky sludge under the manifold where the thermostat rides. The thermostat was also very rusty and stuck open.

Is rust like this on the inside of the cooling passages normal for a boat? Does this indicate salt water use?

I checked for pinholes on the manifold and didn’t see light from a flashlight poking through. I really don’t want to pull the heads, but that looks to be the next step.

Anyone have any insight or ideas?

[Paxdad]

The rust you see in all the passages are normal and don’t look concerning in my opinion. A leak in the exhaust manifold would also cause a misfire so since you confirmed there are no holes you may have a crack in the block somewhere.


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[Paxdad]

Have you checked the drive fluid for signs of water as well?


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[StagNW]

The rust you see in all the passages are normal and don’t look concerning in my opinion. A leak in the exhaust manifold would also cause a misfire so since you confirmed there are no holes you may have a crack in the block somewhere.


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Thank you for the reply. I'm glad the passages aren't concerning. The boat has no drivability issues. There are no signs of water in the drive, fluid is red and clear. '

I don't mind replacing the block, i just hate to change the originality of the boat without a concrete diagnosis.

One theory I've had a few people bring up to me, they keep saying if the thermostat is stuck open, which it has been for a long time, it'll never get hot enough to evaporate the condensation that builds up and it will accumulate. This theory actually seems reasonable to me as there was a high volume of build up under the manifold in the V. I feel like the condensation would stick to the bottom of the intake manifold in the V and mix with oil particles.

I'm thinking about putting it back together and seeing what happens next summer. Whats the worst that could happen? Needing a new block. I suppose time lost off the lake would be the worst that could happen, actually.