[DanElam]

Ok. I oversimplified.

I should have been talking about thermal transfer properties of the coolant instead of boiling and freezing points. Sorry. Bob does, correctly, point out that the freezing points lowers and the boiling points raises if you have enough ethylene glycol (C2H6O2) in your mix. (No, I can't tell you what the ratios are.)

However, as a coolant, the issues are the correct. Water is better at carrying heat than anti-freeze. (For that you can go back to the chemistry books and read. H2O can provide greater thermal agitation of its molecules than ethylene glycol.) Keep in mind that the system isn't exact when it comes to ratios: pressure plays a key part in the boiling points. I think a normal system is about 14psi.

Soooo..... What this all means is that water will carry more heat away, but will boil away sooner than if you have anti-freeze in the coolant. Anti-freeze also has rust inhibitors and other good things, but the real advantage is that it is hard to boil out of your radiator and leave you stranded. Manufacturers compensate by by putting bigger radiators on the cars to move more heat. When you run the car hard, you may exceed the natural/normal ability of the radiator to perform thermal transfer when using anti-freeze. To improve the thermal transfer for both your engine and the radiator, you reduce the anti-freeze (which means more water which has a higher thermal transfer property than the ethylene glycol). Presto! You get a cooler engine.



This physics major shall consider himself properly chastisted and work to refrain from simple answers in the future.


:-)