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This question comes from my next-door neighbor and his ‘79, 302 powered pick-up truck. When he pulled the oil fill cap out, he noticed stuff that looks like mayonnaise on the bottom of it He says, however, that the oil in the crankcase looks okay. Any ideas on what this stuff under the valve cover could be? What should we look for or check?
 

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The wife used to get that on her camaro. We figured that it was moisture from the car sitting to much. The problem stopped when she changed the oil and began driving it regularly. The substance is definately from a water problem.
 

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That is exactly what it is. I have seen it alot. Moisture condensates giving you the milky substance on the oil cap. It might also be on the top of the dipstick. I have seen it alot for some reason on the late 70 and early 80 fords. There is a common problen of the GM quad 4 in which they tell you to take a couple mile drive at highway speeds and it should clear up for a short time. I am not sure of a long term fix though. You might make sure your pcv system is working properly and the crankcase breather element dosen't look like a charcaol briquette.
 

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Too bad it couldn't really be mayonnaise though hu? Saving that extra couple bucks on groceries might be kind of nice.
 

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Even better yet, wouldn't it be great if mayo was the perfect lube. you could have a turkey sandwitch and grease the car in one effort.
 

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Probably condensation, like everyone is saying. But here's a little tidbit for the hard-drive, I've seen the same symptom twice on diesel gen. sets when the apprentice overfilled the oilpan. The crank churns up the oil and aerates it causing the foam. Kind of like putting it in a blender.
my $.02.
 

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This could also be an indication of an internal antifreeze leak, head gasket, intake gasket around water port.
 

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My "project sleeper" at this moment churns up the same stuff you are posting (250-L6 in it right now). It shows no signs of any coolant leak in the oil or oil in the coolant and is running perfectly (daily driver). I've even checked the plugs last week and they are firing normally. This stuff is under the oil cap, the PCV, and on the dipstick when I check the oil (at the proper level, doesn't burn it).

Some technicians that I work with have seen the stuff under the oil cap and they do say it's condensation and doesn't cause any problems with the operation of the vehicle. The car is even getting decent mileage (18-20mpg avg. , 25+ if strictly highway)

Some engines just churn up this stuff more than others. I would just keep an eye on it and clean it out of the oil cap area, PCV system, and even replace the PCV valve and breather more often so it doesn't clogged up the lines.

In the spring my swap will start so I won't have to worry about it when the V8 goes in.
 
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