Oil is milky just around the fill cap

Hi there, so I bought my first car a couple months ago.

As routine maintenance I checked the oil level and it looked a bit on the lower end(actual oil itself looked to be in good shape though), so I went to fill it up with half a liter or so of oil.

Upon unscrewing the oil fill cap I noticed the fluid around and on the cap itself was a milky yellow. Being relatively new to cars I’m not sure if this is definitely coolant leaking into the oil, or if it could just some residue around that area. I also took a video: milky oil fill cap - YouTube

Essentially my question is, should I be worried, and if so what should I do about it?

Thank you so much! :slight_smile:

That usually means the vehicle isn’t driven long enough to drive moisture out of the engine.

Also, if the PCV valve is stuck closed can cause that.



There’s water vapor and oil mist in the engine while it’s running. You’ll get some mixture and deposit on the inside of oil cap, especially in cold weather (condensation.) If you are losing coolant there could be a leak, maybe even head gasket leak, so keep an eye on that.

Thank you so much for the quick replies, I’ll keep an eye on coolant levels and try going for a longer drive before checking it to see if it’s moisture.

Is this mainly used for short trips?

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I suggest that you first clean the oil cap, change the oil, and then take a few long drives before you check it again.

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My guess, you’ve got coolant leaking into the oil. Good ideas above to test first, but if those don’t pan out suggest to ask your shop to do a coolant pressure hold test.

OOPs, took a look at your vdo, and what I’m seeing there doesn’t look like there’s much of a problem. Much less likely than I intimated above that there’s a coolant leak into the oil. Still possible though.

Yeah okay my car is due for an oil change anyway so I’ll just go ahead and do that, then check it again after a few long drives.

I don’t know what you call a long drive but you should check the oil level at least once a week and every fill up of fuel until you have an idea of how much oil this used vehicle uses .

Since you are new to car ownership, I’ll add that changing the engine oil is probably the single best thing you can do for your car. You might decide to defer some maintenance items but suggest to not defer oil & filter changes. Best of luck w/you newly purchased car. Have you check at car rating services like Consumer Reports etc how this vehicle is rated reliabilty-wise, and what its most frequently reported problems have been? Also you could search by its make/model using the forum search feature here, get some ideas what others are saying about it. Give you a heads up if there are any potential systematic problems with the design. Forum search link is above/right this page.

If there was coolant leaking into your oil, the oil on your dipstick would be milky.

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Make sure the oil cap is cleaned after the oil change so you can monitor the situation with a clean slate.


You’re right, oil changes are important and I plan on doing one probably next weekend, just need to get some ramps first. And I have not checked Consumer Reports or this forum as you mentioned for common problems, but I’ll go do that now. Thank you for being helpful and giving me those extra tips :smiley:

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Got one of these, 10 quart, $8.49 now at wally world.

What’s the diameter of that circular opening? When I drain oil, for some reason the stream doesn’t always go in the place I expect it will, plus it starts out going one place, and ends up another. One advantage of a big opening for the drain pan, it helps prevent the oil from going onto the driveway. Plus for catching the oil filter.