Gunk on oil fill cap

Any other symptoms? How many miles? Also how many miles between oil changes?

When I see this my suspicion is oil is not changed often enough and engine is not happy. I usually warn the owner about changing oil more often and just before I change the oil I add a 1/2 quart of "engine flush" and run the engine for couple minutes before draining.

As for all the dust, keeping your car clean inside and out is essential preventative maintenance that will improve your odds of finding problems before they get expensive.

 

Not terrible, but; 1) change the oil more often, 2) replace the PCV valve and check the hose for restriction (or just replace it as well).

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That's pretty minor. More build-up is often found in winter when the engine spends less time at full operating temp.

Often enough all you need to cure it is a weekly 20 mile highway run just to boil the accumulated moisture out of the oil.

 

Really cheap Dino oil with poor oci.

I would expect it’s a bad oil eater.
I take it you never check the dipstick that gunk will be on it too.
Poor oil oci leads to clogged piston rings leads to oil eating leads to destroyed motor from lack of oil. Very common on this site.

The throttle body will be really bad too.

 

I've experienced the same thing in some cars, in much the benign way Leadfoot describes.