A little background first. I noticed a small amount of yellow stuff in my oil filler cap last night. Knowing this is a sign of a blown head gasket I was getting ready to cry, but I did some research and found this site that states it could also be sludge buildup or condensation from short trips. This question and this question both back up the condensation explanation. And I do drive only about a mile and a half to work each day, and it is cooling down, so that is what I am assuming it is.

But, I want to be sure and the site I linked above mentions checking to make sure there isn't any sludge buildup by saying:

Next, shine a flashlight into the valve cover and examine the condition of the valve springs and rocker arms. If they appear clean, you do not have a sludge problem.

I'd like to do this, but I can't see how I can simply shine a light in there and look, does he mean take the valve covers off? That would be a lot of work just to take a quick look.

So my question: Am I missing something? Is there a way to look without taking the valve covers off? Or would I indeed have to remove them to look? If so is there another way to check for sludge buildup?

Follow up question: Should I not be worried about sludge buildup considering my short trips in now cold weather?

Vehicle is a 2001 Dodge Dakota 4.7L if that matters.

2 Answers 2


Short trips do cause condensation which may lead to some build up. To do an adequate job for inspection the covers should come off. That being said I don't think it's necessary. For your driving conditions, it is best to change your oil and filter at least at manufactures recommendations or more. Every six seems to be good to me. Using synthetic oil would also benefit. If you are concerned further you could opt for an engine flush at your next oil change. A blown head gasket can be diagnosed with a compression test.


There is an misunderstanding: There are two kinds of oil sludge.

The dark, semi-solid slurry. That is broken down oil (In a very rough sketch). It is a sign of missed oil changes or present problems with the engine. Black sludge, left uncured, will wear down the engine quickly.

The yellow "mayonnaise". It is a sign of water in the oil. Either the engine is mostly driven cold, or there is water entry in the engine (head gasket or oil heat exchanger, if equipped). Both will increase wear on the engine.

A little bit of mayo under the oil filler cap should be no big issue. Big amounts, especially on other places like the filter, are worrysome. Try a nice long drive on prolonged high load (the so called Italian tuneup). If the mayo is gone you are good.

Black sludge, that is visible through the oil filler cap, is a reason to worry. The best cure would be to take apart the engine, scrape everything off and clean the fine residues with gasoline. Since that is expensive, many people try chemical cleaners with varying results.

  • I will be changing my oil myself in a couple days, if I find no more yellow stuff would you say I can chalk it up to my short commute and just make sure I go on longer drives semi-frequently? Or should I check anything else before assuming that?
    – Mr. Spock
    Commented Nov 19, 2020 at 17:57
  • 1
    Yes, if the goo is gone and no other symptoms exist (Loss of coolant, oil in the coolant, high oil consumption) I'd say that the engine is fine.
    – Martin
    Commented Nov 19, 2020 at 18:58
  • Thanks for the other symptoms I should be looking out for
    – Mr. Spock
    Commented Nov 19, 2020 at 21:00

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