This might help

 

Thanks

 

What does topping of coolant means

 

http://tis.spaghetticoder.org/s/view.pl?1/07/09/65

Checking the level is at the bottom.

Shows how to check the coolant level.
Fill it slowly and check the level often, when you pour coolant in it can push the indicator down and you may overfill it.
Overfilling can lead to a broken expansion tank.

 

fill very slowy and watch the float using only distilled water untill the foat read full do not over fill or this will be sure way u need to replace the tank on the side replace cap. if needed BMW used 50/50 mixture . or even just check to see if the float is in the right stop before filling i had my senor go in mine and sence it said it was low i over filled it not good idear.