Mark Hodowanec

When running the defog drop MPG? The AC comes on when you have the vent on defog so, wouldn't the mpg drop? How much?

tbarbee1

I have no idea how much but yes it increases drag on the motor so one would think that the MPG would drop I doubt its a measureable difference.

ColdCase

I don't think the AC compressor "drag" is as much in the cooler weather you typically run the defog as in the mid summer heat... but I don't recall reading how much that means to mpg.

ratlratl

Around here it is so humid, that I seem to run it all the time. I'm sure there is a difference, but to me it is the convienence factor that outweighs the mileage loss. However slight it may be. All of my diesels have progressively gotten worse mileage, so as long as the current one gives me 17-18 I'm happy. When other people I know with their gas trucks brag about their 350 horse V-8's getting 13 or less or a big block chevy guy getting 9 . It just makes it all the less noticeable. Plus I can move their house.

Chris

sabersix

Somehow with 650 ft/lbs of torque, I don't think the A/C compressor adds any appreciable load...

TTDiesel

What does how much engine torque you have matter? The ac compressor still puts the same load on the engine. You may notice the load more if you only have 500 ft lbs vs 650 lb but the decrease in fuel ecomony not matter how small would still be the same.

Spooler

Very minimal. I run my A/C all the time including the winter time except for maybe 2 weeks out of the year when it is cold around here. Fuel mileage is about the same. Never noticed any difference.