Quote:
Originally Posted by Duffman
I would think any loss in fuel economy as you get in the super hot region would be due to increased A/C usage. All fluids get thinner as they get hotter and the engine pumping losses are less in the heat. The air you are pushing should be thinner too.
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I agree, the only negative factors in high temperatures are:
-A/C usage (a huge decrease depending on your car)
-Slightly more rolling resistance due to softer tires
-Possible fan loading if engine temps get too high
-summer blend fule
Overall, between air density and fluid viscosity, heat is better than cold hands down for FE, that is assuming you sweat it out with your AC off and widows up!