Fuel Economy Tip – Don’t Run Your Defrost to Get Rid of Morning Dew

Today’s tip will help you increase your car’s fuel economy as well as help to keep you save when you start your morning drive.

Don’t use the defrost to get rid of morning dew – use a rag instead.

Obviously, if you park your car in a garage, this isn’t going to be much of a problem.  However, for those of us who park our cars in the driveway or in a parking spot, morning dew can be kind of annoying.  Unfortunately, I think many people go about getting rid of it the wrong way.

What many people do is start their car and let it idle, while they crank up the defrost and “burn” the morning dew off their car windows.  As I’m sure you’ve already guessed, this is bad for two reasons:

  1. You’re wasting a lot of gas by simply letting your car idle
  2. By running the defrost, you’ve turned on your car’s air conditioning, which uses even more gas.

Instead of doing the above, all you really have to do is take 30 seconds and wipe down the windows with a rag or an old cloth.  It’ll do the same job and ultimately use a lot less gas.

Don’t misconstrue this as you shouldn’t ever use your defrost; if you’re driving and you need to quickly use the defrost to clear your windshield, by all means do it.  However, make sure you wipe down your windows first, that way you only have to use the defrost for a short amount of time.


  1. I’ve been reading and collecting mileage tips for a very long time and never saw this one before. Great tip. Most people don’t realize the defroster on most newer vehicles turns on their air conditioneer compressor.

  2. Brian Carr says:

    Thanks for the comment. As I’m sure you can see, now that I’ve gotten past all of the obvious tips, I’ve had to start to become quite creative to continue to come up with new tips!

    I agree with your assessment that most people fail to realize that when they turn on their defrost they’re actually turning on their AC. I would imagine most people think the defrost directs hot vent air.

  3. Would you please settle a disagreement?

    I think that when you use your defrost in your car, you are using more gas because the air conditioning and the defrost run off the same compressor. Even for older or newer models?

    Does this same concept work if you don’t have air conditioning? Does it still use up more gas if using the defrost because your car still has a compressor?

    If I’m right and your car uses more gas whether or not you have a newer or older model or whether or not you have air conditioning, would you please explain in detail how and why this concept applies or doesn’t apply?

    Thank you.

  4. Brian Carr says:


    Thanks for the question. To the best of my knowledge, if you run your defrost in a car that does not have air conditioning, it won’t result in worse gas mileage. Essentially, it would be the same thing as using the vent and blowing hot air on your windshield.

    In terms of newer vs. older cars, newer cars are made to be more efficient when it comes to this kind of stuff, so they will typically get better gas mileage when using the air conditioning.

    Hope this helps.

  5. Something needs to be clarified, we’re talking about the front windshield defrost right?
    Not the rear.
    I don’t see how turning it on for 20 seconds is going to make the slightest change in your fuel economy. I also find that using AC instead of windows rolled down and keeping the vents open when not using the AC gives me better mileage.

  6. I’ve heard that using the AC with heat on actually makes it more fuel economic? am I crazy?

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