I just had the oil changed in my 2006 GMC 2500HD Duramax diesel, my truck has 56,000. miles on it. The oil look on the dip stick looks really black! I feel like it wasn't changed at all.

What should the oil look like. I have always thought it should look clean, that has been my experience with my other trucks. I have also driven it 100 mile since the change.

  • There will always be some oil left behind in the engine during an oil change. This will mix with the new oil and make it look dark. Two things. First, look at the oil before it's changed to ensure it looks different after. Second, you can always change the oil yourself ... that way there is no doubt about it. Oct 2, 2016 at 15:19
  • Sounds like you are new to diesel ownership. Be sure to read your owners manual regarding the service interval. You'll be doing fuel filter changes more regularly, among other things.
    – cory
    Oct 3, 2016 at 14:25

1 Answer 1


Totally black almost immediately. Diesel engines produce a lot of fine soot which the oil is formulated to pick up.

In a gasoline engine the oil will behave like you're expecting, gradually darkening as carbon builds up over many miles. Diesels are very different in this regard. The oil turns black very quickly. I think 100 miles is plenty for it to be very noticeably black.

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