Thread: Coolant Warning
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      01-13-2012, 08:56 PM   #17
paul386
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Drives: 2011 X3 35i Jet Black
Join Date: Oct 2009
Location: Florida

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Quote:
Originally Posted by Lotus7 View Post
Paul, Don't know where you got your expansion values, but the change in density, hence the volume of a 50/50 mix going from 30deg. F to 80 deg. F. is actually around +0.98%. BMW still uses ethylene glycol based anti-freeze and the temperature expansion curve is complex (it's a quadratic polynomial). (The density of 50% ethylene glycol/50% water is about 1.081@ 0deg. C and about 1.071 at 25 deg. C.)

The total coolant volume for the 35i does not seem to be listed on any spec sheet I've seen. Considering the engine, [large] radiator and heater sizes, I'd guess that it's no more than 10 quarts (9463 cc). Given that volume, the thermal contraction (due to ambient temps only) will amount to about 93 cc. (or less than my earlier estimate). That means that my 35i probably actually lost about 350 cc in 7500 miles.
Yeah I probably made a mistake in using the ideal gas law. I'm a structures guy, leave me alone.
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