BMW Oil Filler Cap Leak - E90

The seal in the BMW oil filler cap will begin to harden and deteriorate which allows oil to leak. Judging by the amount of posts I see in BMW forums, this seems to be a very common issue.

To stop the leaking:

1. Buy and replace the oil filler cap. The new cap comes with a seal. 
• Part # 11128507153 for E9X BMWs with the round oil filler cap. Earlier E90, E60, E85, and late model E46s use this square oil filler cap.
• Part # 11127509328 for earlier model BMWs with the square oil filler cap.  
2. Carefully remove the existing seal. Clean and reinstall by reversing the ring. I would only try this if the leak is very small and I don't want to spend $15.

My leaking oil filler cap:  

I changed my oil and the oil level read max in iDrive. A couple of weeks later, the oil level dropped and it didn't seem right that I would lose oil that quickly.

I noticed dried oil around the oil filler cap and oil leaking down onto the valve cover area. I pulled my oil cap and it looked like mustard. After doing some research and asking some friends, I came to the conclusion that my oil filler seal was bad and condensation was coming in and mixing with the oil and looking like mustard on the cap. I replaced the oil filler cap and oil consumption is now normal and no more weird mustard looking oil under the cap.

Below is what my old oil cap looks like and the seal that is indented. There is caked oil all around.