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Old 10-05-2012, 10:09 AM   #81
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Join Date: Sep 2012
Location: Old Greg's Cavern
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My Ride: '13 128i, '04 330Ci
Originally Posted by joegr View Post
So, all this theory is interesting, but I wonder if something is being missed in practice?

I have three other cars that have 15 PSI relief caps. Once heated up, I can squeeze on a radiator hose and tell that the system is pressurized, but not how much. On the BMW, when I squeeze on the hose (once heated up), there is noticeably more resistance to squeezing than the other cars. To me, this implies that it is indeed pressurized to a higher pressure than the other cars I have.

We can speculate about this, but I suggest that it is easy to find out for certain. Just tap a small pressure gauge in and find out what pressure it goes to. It seems like the bleed screw on the upper radiator hose would be a good place to do it. It would be a sacrifice of a $25 hose, so not too bad.
The hose on our BMW may just be more stiff than other cars too. Also, I have no doubt that the output side of the pump (that hose) will be at a higher pressure than the rest of the system. This is where a flow sim would help, but I don't have enough data. Tapping a place for a pressure sensor/gauge is hard, because you will likely weaken the connection. You could cause a part to crack open.
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