Quote Originally Posted by 89Vette View Post
What's more interesting (maybe) is that I went from 14.2 to 15.1 when I replaced my u-joints. I could actually tell the vehicle rolled smoother and definitely was quieter. I'm not surprised it improved, but I was surprised at the amount. I think part of the improvement was due to an increase in outside temps though.
Anything you fix/replace that makes a noticable difference in how the vehicle rolls should improve your mileage for sure.

But temperature-wise, cold air is better than warm air for performance and efficiency. It's VERY noticeable at 5500 feet here in Denver. I always get worse mileage in the summer (assuming my heavy right foot is the constant) at 90F vs winter at 30F. Hot air = less O2 per cubic foot intake = engine has to work harder to produce the same amount of power. Hence so many "cold air intake" kits.

I suppose that could be offset by warm temps making things roll and lubricate more easily, but that just gets back in to the "too many variables to tell" category.

Basically, we get crap mileage no matter what we do. Plus it's all relative to what you're used to and what you're willing to stomach.