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Recently there has been a lot of fog on all of the windows in the car, particularly on my windshield. It's been bad enough that I've had to stop and wipe the glass off, but the fog can come back during a drive.

What can cause all of this fog on the windshield? What things can I try myself, before taking it to the shop?

I have a 2002 Subaru Forester.

Scott Hillson
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KatieK
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3 Answers3

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Typically the fog is from excessive humidity in the vehicle. The three most common sources I can think of are:

  • A leak that allows rain water to collect in the car. Check to see if the rugs are damp, look in the storage well behind the seat and any place water might collect.
  • Do you also notice a sweet smell when the engine gets warm? If you do it may be a leaking heater core. Antifreeze could be leaking into the heater box then the vapor is fogging the windshield. Antifreeze residue can be difficult to remove from the windshield. Try rubbing a clean tissue on the inside of the glass. The tissue may show the oily component of the antifreeze.It may be a small leak as a little antifreeze goes along way in terms of fogging the glass.
  • The third source could be the A/C. The A/C unit removes humidity from the air. This is what causes the puddle under the car when the A/C is running. Sometimes the drain get clogged with leaves or pine needles. This allows the water to build up which adds humidity when you run the defroster. If enough has collected you may hear it sloshing under the dash when you make a turn.
Rory Alsop
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mikes
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6

You don't have the air inlet selection lever set to recirculate, do you?

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Jeremy Stein
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If you have an a/c, you can leave it on even if you have the heat on and it will clear the fog. Wipe down the inside of your windows with windex, that will also help.

Scott Hillson
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