true or false:

it lowers your mpg the same amount to use the AC at it's lowest setting and highest setting.


and


it lowers your mpg the same amount to use the heater at it's lowest setting and highest setting.

 

Yes.

 

I guess you learn something new everyday. I didn't know running the heater put a load on the engine.

 

Running the heater will NOT make the engine use more fuel. All it does is turn on the fan on the SECOND radiator, which is next to the firewall. If you watch in-camera of races, you'll see that the driver may turn on the heater if the engine temp gets too high.

There's a debate on the A/C part. A/C DOES waste more gas, but on some cars, opening the windows messes up the drag coefficient so much that it would be better to use the A/C instead. As for losing the same mpg between lowest and highest setting; I'm sure its not, but at the same time, it would be such a small difference to notice.

 

^^^
I guess you can unlearn something new everyday. I thought the heater core was just a second radiator with a fan as you said. The water pump is spun anyway, heater on or not, and that is the part that draws a load.

 

Running the heater may actually help your car, albeit very little. Running the extra radiator (heater core) will cool the car better, possibly resulting in more efficiency. The AC on the other hand, places an extra load on the car. I'd think that running it on low (not fan speed, but at a higher temperature) might be less taxing than running it full blast, at least on a car with automatic climate control, because the compressor will not have to run constantly, just enough to keep the interior at the specified temperature (much like setting your house thermostat at 75 in the summer instead of 65).

 

Modern AC compressors are so efficient that they have little impact on mileage and as mentioned can actually help improve mileage if you leave windows up reducing drag. The heat will have no impact on mileage but some defog settings dehumidify the air with the AC, but still the impact is so small you will see no difference.

 

Both the AC and heater use additonal fuel. There is no argument there. What is arguable is to what degree they use additional fuel by making the alternator draw a little more charge. And to what degree you have the AC on [fans on low, high, etc.] also effects fuel mileage, this isn't arguable. To claim so is to claim that requiring the car to expense additonal energy doesn't require additonal energy input. It's not worth wasting your time about though, if it's cold use the damn heater. If it's hot and you don't want to be sweaty at work, you should probably use the AC.

 

kinda of a variety of responses. can we get a conclusion?

 

There was a Myth Busters episode about AC vs Windows down.

The conclusion was the Windows Down uses less gas than AC on the SUV they did the test on. The test was fairly thorough and the Windows Down car ran significantly longer on the given amount of fuel than the car with AC from what I recall.

I don't think there was a test for the heater though...