There are a couple of ways to open the oil cap on a BMW. These steps show you how to do it.
The first step in opening the oil cap on a BMW is to take off the plastic trim. To do this, grab onto one of the ridged edges and pull towards the back of the car slightly. Repeat this for all 4 trims until they are removed completely from the car’s body. This should expose the oil cap.

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The next step is to locate the oil dipstick. The dipstick is a long, metal stick that will be sticking out of the top of the engine. The BMW logo should be facing upwards. There is a small, black ring around the top of the dipstick.

This is your indicator of where the oil level should be.

Now that you have located the oil dipstick, take the cap off of it by twisting it counterclockwise. Be careful not to touch the dipstick with your hands, as this will contaminate the oil. Place the cap somewhere safe where it will not get lost.

Finally, grab onto the oil dipstick and pull it out of the engine. Look at the oil level on the dipstick, and make sure that it is somewhere in the middle of the black indicator ring. If necessary, add or remove some oil from your car before inserting the oil dipstick back into its holder.

Make sure to push down on the stick until you feel a click. The click means that the oil is now being read by the car. Pull out your dipstick and check to see that it reads at or near the middle of the black ring as before. If it is, you’re all done. Following the steps above should open your BMW’s oil cap and allow you to check the oil level of your vehicle.