I would like to know if the 2005 Highlander Air Conditioning consumes gas at a lesser rate when the car is kept at 80 degrees versus say, 65 degrees. This assumes that I am using AUTO. Anyone out there have experience?

 

We all own vehicles that are designed to go off road.

You might find better luck at one of these forums or simply calling your Toyota dealership...
http://www.toyotanation.com/forum/f83
http://www.tundrasolutions.com/forums/

 

Theoretically, yes it would. AC uses gas to run the compressor so the less it runs the less gas you'll use. Whether you'll notice a measurable difference I don't know, but there is one easy way to find out. Run for a couple of weeks at each temp and check your mileage.

 

Old rule of thumb is that at highway speeds, you are lessening drag by keeping your windows up. Since accelerating uses the most gas (as opposed to cruising speeds), theoretically when the AC is on, and you are moving at a constant rate of speed, you use less gas by using the AC. As soon as you accelerate, however, your fuel economy drops. This is why the EPA has different levels for "highway" and "city" driving. For example, I got about 19-20 mpg on a 150 mile highway trip. But normal driving, I'm hitting about 14mpg. Thats with and without AC, respectly.