Bimmerfest - BMW Forums - View Single Post - Got the 1.2 bar expansion tank cap from German Auto Solutions
View Single Post
Old 08-04-2013, 05:27 PM
gary@germanautosolutions's Avatar
gary@germanautosolutions gary@germanautosolutions is offline
'Fest Sponsor
Location: Grand Rapids, Michigan
Join Date: Jul 2010
Posts: 425
Mein Auto: E39 528i, E60 M5
I understood everything you said about the pressure cap, but, I just can't make sense out of the hose flow explanation.
Since the hose is attached the highest point in the system, and has a bleed screw port, it's the last and best place to bleed any remaining trapped air in the system.

The passage that the hose connects to enters a separate circuit between the two o-rings on the coolant cap. This is the return path of that hose flow into the expansion tank. Since this hose is passing coolant during normal operation, and that coolant passes through the cap just below the pressure relief valve, if the system pressure exceeds the cap rating, when the cap vents that pressure, it will vent both air and coolant.

This system helps to vent any steam first if the system has actually overheated, because the stream will enter the system at the top of the radiator. But also helps to rid the system of excess coolant if the excess pressure is caused by overfilling the expansion tank.

I hope this helps.


"I'm a little rascal on my Little Rascal"
- unknown
Reply With Quote