Possibly cavitated engine?

[habaneropep2019]

Dug deeper into my troubled engine (low compression on #4 and #6, 100-150 psi lower than other cylinders). Pulled the valve cover off and was greeted with this lovely sludge mess.

Did a leakage test and determined it is primarily leaking past the intake valves, though there is some small leakage past the exhaust on one cylinder. No pressure in cooling system at TDC on either suspect cylinder.

Then I dropped cylinders to BDC and loosened the rockers so valves would stay shut. Applied shop air, and lo and behold cylinder number #4 pressurized the cooling system.

While I know the valves leaking is definitely the cause of low compression, I’m worried that the cooling system pressurizing on the bottom of the stroke is indicating cavitation on that cylinder. If it was a blown head gasket I would expect it to pressurize at TDC as well, and that did not seem to be the case. The engine was low on coolant when I got it with no external leaks that I could find when warmed up, so I suspect coolant has gone somewhere internally.

Thoughts?

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[ihc1470]

Pull the oil drain plug and see what comes out. You can unthread it and hold it against the pan. You should not loose that much oil and water will come out first if there.

 

[habaneropep2019]

Pull the oil drain plug and see what comes out. You can unthread it and hold it against the pan. You should not loose that much oil and water will come out first if there.

When I changed the oil it was overfull by a decent amount. There wasn’t water at the bottom but it may have been mixed in from running. I don’t think it had fuel in the oil, I know the smell of that.

 

[DaveBen]

It will look milky if oil and water are mixed together.

 

[scsmith42]

Sounds like a cracked cylinder at the bottom of #4.

 

[ihc1470]

Let is sit for a few days and crack the plug again and see what you find. This is if you have the coolant full.