Creamy film under engine oil cap?

It's not ALWAYS head gasket. Lots of short trips, rainy weather, I've seen that once or twice, on older cars we've had. High air humidity contributes.

 

Water vapor/condensation is a normal by-product of the combustion process. I think this is a sign of that + an oil change interval that is too long for a vehicle that isn't getting to full temp often enough.

 

If the coolant level in reservoir is stable that's a good sign.

 

That looks like moisture to me (water or coolant).

1) Since oil change is due in 1.5K miles, I'd change it today.
2) As mentioned, if coolant tank is still full that is a good sign.
3) The moisture could very well be from short trips and weather conditions and not an issue.

FWIW
Give a good look around the engine bay checking all the lines/ hoses and containers.
Could be from power washer the engine bay.
Check the seal on the oil fill cap and dip stick filler tube.
If you wanted to go further, I would wait until 1K mileage after the oil change.
Then you could remove the spark plugs, use a cameras to inspect the tops of the pistons and/ or do a leak down and compression test

Good luck.

 

In a case like this, it needs a cooling system pressure leak-down test.
The leak down test that usually goes along with a compression test is something different.

 

Also not yet mentioned, is the corn lobby has pushed water absorbing ethanol into 10% of our gas. This has been done over the dubious claim of being cleaner burning, but profit for the corn industry is the real motivation of it and ethanol also has been shown to damage engines with a build up of laminates. This water in the fuel issue is also why people can't get their lawnmower started each Spring, a huge money maker for lawnmower repair businesses.

So if you can find access to Non-Ethanol fuel in your state, that'd help address what you're seeing on your oil cap.

 

What is the mileage on the car and where are you getting your oil changed and what kind of oil do you use.

The coolant overflow tank is useless to gauge the level of coolant in the engine on this car.
It could be full and the radiator dry.

Take the plastic cover off the top of the rad the rad cap is under it.
Leave the screws off the cover just fit it back on. Mine has been loose for 12 years. The hood traps it.
Now I can quickly and routinely see what is actually in the engine.

 

Total BS. Just stop it, please.

 

Its moisture. If you whip oil and water together you get what looks like a milk shake. Water in engine oil looks like a chocolate milk shake and water in trans oil looks like strawberry (or Pepto Bismol).

I changed the valve cover gaskets on my old 72 F100 and the underside of each one had a qtr inch build up of that sludge on them. From what I've read the moisture is probably due to short trips which my pickup gets a lot of. I've never seen it in any of my other vehicles except for the old Volvo we had that sprung a leak inside the trans cooler and my radiator was full of what looked like Pepto Bismol. The water destroyed the tranny.

It's no sweat if all you only see it on your oil cap and your engine oil is normal. If your engine oil looks like a chocolate milkshake then you have a problem.

 

If the coolant level in the radiator and surge tank are both stable, and the oil condition looks reasonable for the mileage (not "creamy" tan/gray or "coffee with milk" color) then I might consider it "normal" condensation build up in an engine that has too much short trip driving or isn't getting up to full operating temperature.

I would suggest getting the oil and filter changed, have the PCV valve replaced (and the vacuum and breather hoses inspected or replaced), and have thermostat function tested.

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