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I accidentally put 6 qts of ATF in my diesel engine. Ran for just a few minutes until I realized what I did. Drained all ATF and replaced with engine oil. What else should I do?

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    At this point what else can you do? My guess is that you'll be ok. ATF is a lubricating oil and while it's not rated for use in diesel engines, it's not like you put water in there. If there has been damage, you'll eventually find out about it. I would not proactively teardown and rebuild this engine on account of this.
    – jwh20
    Jun 22, 2021 at 15:41
  • ATF has a lot of various detergents in it along with the oil - since you drained it all out you've probably done more good than harm. I've thrown ATF through really gunky poorly maintained engines before for exactly this reason, just run and flush. As you mentioned in a further down comment, just change out the filter because it will likely have loosened up some crud out of the engine.
    – Aaron Lavers
    Jun 23, 2021 at 2:35
  • @AaronLavers changing the filter was mentioned in the answer.
    – Solar Mike
    Jun 23, 2021 at 4:14
  • How new is the diesel engine? I assume it is for a car (not, say, a tractor or old fashion harvester?). If it is old, pre common-rail and computerized injectors, it is less of a problem. It'll smoke and complain for a while... If it is newer than that, the answer you got is spot on.
    – Stian
    Jun 23, 2021 at 6:55
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    @AaronLavers compared to modern engine oils ATF likely has a lower detergent level. You're correct in terms of some stuff potentially being loosened though - since ATF is thinner than regular oil that can have a flushing effect.
    – motosubatsu
    Jun 23, 2021 at 9:06

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I would run the engine again for a few minutes and then drain that engine oil as it will have any ATF that was still in the galleries.

Then fit a new filter and refill with fresh oil.

After that you should be good to go.

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    Thank you for your advice! I was thinking about changing the oil & filter, as suggested, after driving a little bit. Just wondering if this would be just precautionary slash overkill, or if this would be a critical idea?
    – Tony
    Jun 22, 2021 at 16:57
  • @Tony given the relative cost of an oil change vs a replacement engine, even if not doing so is only a low risk is it really one you want to take?
    – Dan Is Fiddling By Firelight
    Jun 23, 2021 at 13:05
  • @Tony Probably overkill, but it may be worth the piece of mind. Only a small fraction of ATF will remain after a drain/refill. Even if 0.5 quarts were left out of 6.0 qts, it would only lower your oil viscosity a small amount (ATF is effectively 0w-20 weight, I assume your motor oil is 5w-40), probably not enough to matter.
    – masospaghetti
    Jun 23, 2021 at 16:01

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