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View Full Version : How does the coolant expansion tank work?


Dave1027
02-14-2013, 11:26 AM
Every vehicle I have owned (except this bimmer) has been pretty simple as far as the expansion tank goes. A hose is connected to the radiator cap neck. When radiator pressure exceeds a point (determined by the cap spring) it allows coolant to pass to the expansion tank where it is available to be "sucked" back in when the pressure reverses. Under normal conditions, the radiator is completely full of coolant and the level is checked in the expansion tank.

I do not believe the bimmer works that way. The fact that these tanks are prone to failure indicates the tank is also pressurized. If so why is it designed this way? Can somebody post a description of how the radiator/tank works?
Rovert
02-15-2013, 08:52 AM
I think that the ET helps to create 1 bar of pressure to change the boiling point of the coolant because BMW engines run hotter than usual. I'm not totally sure but I think that's the main use of the ET. I know others know a vast amount of knowledge more than myself. I've got headaches trying to understand all their mathematical forumlas on pressure...LOL
ryankokesh
02-15-2013, 08:55 AM
Short answer: it doesn't work.
Dave1027
02-15-2013, 09:16 AM
I guess I should edit my original post. Other manufacturers call their tanks "overflow tanks". I'm guessing BMW decided to integrate the radiator and overflow tank into one unit. Searching on the subject I found the common failure to be on the heater hose connection cracking from stress heater hose flexing.
alexandre
02-15-2013, 09:50 AM
Short answer: it doesn't work.

:rofl
SoCalZman
02-15-2013, 10:13 AM
Well, I was just reading about this in another thread and apparently G.A.S. has a new ET cap that releases pressure at 1.2 bar instead of 2 and this is might help relieve some stress on these cooling components.
Dave1027
02-15-2013, 12:17 PM
Well, I was just reading about this in another thread and apparently G.A.S. has a new ET cap that releases pressure at 1.2 bar instead of 2 and this is might help relieve some stress on these cooling components.

Nice. I'm getting that along with the DISA repair kit. They have a combo deal.