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Old 11-18-2012, 11:18 AM   #2365
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Originally Posted by chicagocpo View Post
How about the first law of thermodynamics? I'm thinking about reduced mileage in cold weather AFTER the car warms up, that would have greater relative effect on longer trips. "Heat and work are forms of energy transfer." So, colder temperature would mean more energy used to maintain the engine at running temperature, leaving less for the "work" of moving the car once it got there.

Maybe there is a physicist out there who could comment on this?
When detonation occurs, some of the energy is converted to expansion, which powers the cylinders. Most of the energy is converted to heat, which is waste energy, doesn't contribute to powering the car. It doesn't matter if it's 32 degrees outside or 100 degrees, detonation will produce mostly waste heat in excess of what's needed to maintain the engine at optimal running temperature. So, no, in cold weather, the chemical reaction doesn't change to produce more heat and less expansion. The gas isn't "smart" that way.

Mostly, in cold weather, you have the issues that others have pointed out: fluids are thicker and take much longer to warm up, so have more resistance and take more power to move engine parts in contact with the fluids.

And then there's the winter gas issue:
According to this, winter gas has more butane, which has less energy, resulting in up to 1.7% lower energy output.

(Not a physicist).
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