Quote:
Originally Posted by rak299
You may be right, but I don't know what concentration got installed at the factory. I will pretend that BMW coolant has a boiling point of 180C and water boils at 100C. If we assume the correct liquid is a 75/25 mixture (25% water), it would boil at 160C without a cap installed and vent at about 175C with the pressure cap. If some cars got produced with 50% water, it would lower the temperatures to 140C without a cap and vent at 155C with a cap. Normal coolant temperature under load might be 160C. In that case, it would vent (evaporate) with the wrong mixture and not vent when the concentration is raised. I know that coolant is normally heated above the normal boiling point because I know someone (not very bright) who got badly burned trying to remove a cap before the engine cooled down.
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Yes that is why it is pressurized to raise the boiling point.