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Old 01-18-2013, 04:18 PM   #181
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Join Date: Feb 2008
Location: Philadelphia
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My Ride: M3 & ZHP
Originally Posted by mkodama View Post
Good info kmulder!

Seems mostly like BMW just opted to have the expansion tank cap act more like an emergency vent valve, and also probably taking into account people using just plain water and at high altitude which lowers everything slightly. It would be nice to know when problems of boiling actually start but that would probably be pretty hard to test.

And also filling to the minimum will be the most dangerous for risking boiling and warping in an overheating situation.

I don't think any government cares about evaporated water.
They might care about the little bit of antifreeze that's released (you've never seen the little bit of dried coolant near the cap?). Net impact is probably minimal, but they do seem to care how much of it makes it into the water eventually. I wouldn't put it past various environmentally inclined lawmakers to demand such measures.

Maybe there's some other reason. But if 2-bar is seldom achieved... Then I can't think of one. Seems like the 1.4 bar caps used on older vehicles would maintain enough of a safety margin for those who don't run the right mixtures.

Last edited by TerraPhantm; 01-18-2013 at 04:20 PM.
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