I accidentally placed engin oil in the atf reservoir in a BMW 520d. How do I fix it? I have to ask that what effect on my car and how i remove all the ATF oil and how to refil new oil.

BMW E39, 520d, Model 2001


  • Before you drive it, drain all the transmission fluid and refill it with the proper fluid. I would imagine the effects would not be good considering they are likely of different viscosity, have different detergents, and motor oil will break down much faster than ATF. – Poisson Fish Oct 29 '15 at 21:33
  • can you tell me how can i drain all the transmission fluid from ATF container and all the system. have you any video or have on youtubbe. please let me know. – Qamar Oct 29 '15 at 21:45
  • I'm not finding anything for your specific model, but there is a Youtube video series that might help. Follow the links for Part 1 and Part 2. – Poisson Fish Oct 29 '15 at 22:15
  • 2
    How much did you put in? Is it just in the reservoir? If so, you may be able to disconnect the pipe that connects to the transmission and just flush the reservoir. – HandyHowie Oct 29 '15 at 22:34
  • can you reach through the Internet and do it for me too? Sheesh guy, you can search youtube just like the next guy... – Nick G Nov 10 '15 at 22:49

I recently put engine oil in my power steering fluid reservoir. Power steering fluid is similar to transmission fluid. It mixed in fine and had no effect that I could identify. Due to a leak I eventually ran my power steering on pure engine oil until its was repaired.

Oils and transmission and break fluids are hydraulic fluids and apart from different viscosity they will perform similar.

But transmissions are designed for a particular fluid type and other fluid mixtures will change viscosity which I suspect will change gearbox behavior and efficiency. More of a concern is that seals may not be designed for mineral or synthetic engine oils.

If I had done this, I would see what effect it does have for all our benefit and then drain and replace with correct fluid.

  • The example that you describe is not at all the same. This is not an answer to the question. – Bob Cross Nov 5 '15 at 12:50
  • Bob Cross, I agree that it is not an answer... but how many people can actually answer OP's question "... what effect on my car" from experience? I have some experience with same type of hydraulic fluid and engine oil, but not in a gear box. – philcolbourn Nov 22 '15 at 15:02
  • @philcolbourn. Have you ever looked inside the valve block of an automatic transmission? There is no way engine oil will flow through the very small channels the way auto transmission fluid will. – HandyHowie Nov 23 '15 at 19:04
  • I have, I helped my dad service a borg warner 3 speed auto from 1970's. I recall channels. They seemed to be about size of a drinking straw. Are these channels smaller on new transmissions? – philcolbourn Nov 26 '15 at 22:08

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