5-Series (E12,E28, E34, E39, E60)Chat relating to the BMW 5-Series of all generations. Specific models include: BMW 518, BMW 520, BMW 520i, BMW 530i, BMW 528i, BMW 530i, BMW 518i, BMW 524d, BMW 525i, BMW 525e, BMW 528e, BMW 540i, BMW 535i, BMW 520d, BMW 525td, BMW 525d, BMW 530d, BMW 525i/xi, BMW 530i/xi. (BMW 5-Series Forum)
If you have a small tube that snakes its way across the top of the radiator to the expansion tank, check to make sure it isn't twisted or kinked. This tube bleeds air out of the system to the expansion tank and if this hose is kinked the trapped air affects the operation of the cooling system. Worth a look if its applicable.
You could simply have an air lock !
Slacken the pipes to the heater matrix to see if any air/bubbles come out ...
Try lifting the front of the car as high as you dare when topping the coolant up, this will help clear air out of the system (run engine while you do this !!).
Maybe put a small bottle of K-Seal in the coolant too !
Just an idea... Good luck :-)
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