I've heard that both A/C and Overdrive bring down gas mileage.
Personally, I think Overdrive would help gas mileage, because (as far as I know, I may be wrong) it just allows the transmission to go into 4th gear. A 4th gear would help decrease RPM, and therefore help gas mileage? Am I wrong? I really don't know that much about what Overdrive does if not just allowing the use of the 4th gear.
The other thing is with the A/C I don't understand how it affects gas milage. The compressor is belt driven, and its not like the compressor itself consumes gas. Since the belt is always going to spin whether the A/C is on or not, I don't see how it can affect gas mileage. I understand the pully will only spin if the A/C or Defroster is on, but does the amount of force needed to rotate a pully really affect gas mileage? Or is there something else I'm missing.
I may be wrong in both cases, but with what I know it doesn't seem to make sense, maybe I'm naive and missing something. If anyone can confirm if they are myths or facts, please give reasons along with it.
Thank you
Russ