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Fogging windows

I have a 2001 Chevy Malibu LS that I bought in 2004. Last winter it developed a fogging issue. When the temperature drops the inside of the windows fog up, starting in the back and moving forward. I have to run the defrost on full to get it to make a dent on the windshield and even then it leaves a heart shape that’s cleared. It has no apparent trigger either. The other day I had the car out and warmed up for about 15 minutes and it started fogging up. Last winter it was typically worst on the day after a snow storm.

I’ve been to three garages about it. One said there was a hole in the floorboards, one said it was a problem with the air conditioning and the third just really didn’t know. This becomes something of a safety issue when it gets really cold because the fog built up on the windows will freeze over so I have to roll down the windows to see. Please help!

It sounds like you have too much humidity in your car. Possible causes: (1) leaking heater core, (2) clogged AC drain, (3) soaked carpet, (4) you have an operational humidifier in your car, or (5) you sweat way too much.

You need to bring in outside air. It also helps to heat the air. Do not use the “recirc” button. Are you doing all this?

As Tardis said, there’s too much humidity in the car. You may have a source of excessive humdity.
As Lars said, you need to be circulating in new air and it needs to be heated.

However, I’m going to suggest that since it’s a new problem and since it’s freezing on the windshield you have a problem with the heating system as well as perhaps the AC system. It’s also possible, and I suspect this, that your engine isn’t heating up properly, perhaps due to a thermostat stuck open.

The way the system should work is that air dried by the AC systm’s evaporator gets heated by the heat from the engine’s coolant, creating warm air with low relative humidity. When it blows out the defrost vents, it heats the surface of the glass and it, having low RH, also picks up moisture. There should be plenty of heat for this action to take place. If the glass is icing up, there clearly is not. Therefore, I’d suggest starting by checking the engine’s cooling system for proper operation.

Remember, the thermostat’s function is not to allow the engine to cool, but rather to allow it to reach operating temperature. It’ll cool great without the T-stat, but it will never heat up.

I probably should have added too that this problem has occurred with two engines. I put a new one in back in April. (yea that was fun)

Now, obviously I’m not all that knowledgeable about engines but wouldn’t a thermostat not functioning properly be something that would get checked rather quickly? I get great heat out of the vents all over the car. I spent a lot of time last year running from garage to garage trying to figure this out so it will be rather aggravating if I’ve put up with this for so long and it turns out to be a simple thing.


Just have to add this… no car I have ever driven has allowed you to run the defrost and have it on recirculate. I drove home tonight with the back windows down (and me shivering up front) and it made no difference to the fogging. (It was above freezing tonight, but just barely!) Thanks!

There’s water in the car somewhere. Lift the carpet edges (easier said than done) and feel underneath. Is the padding wet? Check all over the interior, then open the trunk and check under the mat.

There’s water somewhere, and you have to find it before you can dry it out and stop your windows from fogging.

If someone were looking at the defrost system problem they would not necessarily look at the T-stat. However, your statement that you get great heat out of the vents sort of negates my idea anyway.

If you’re getting great heat out of the system and the windshield is icing up, perhaps the doors that deflect the heat to the defrost vents aren’t functioning.

THIS is the one that I like, because he mentions the trunk.

If you open your trunk and look in the spare tire well, I’d almost bet that you’ll find a puddle of water. Because your fogging issue starts in the back, I’m guessing that you have moisture in the trunk, and as the car warms up (much faster at the front), the gradual warming at the rear causes the humidity.

Check out that trunk, check out the spare tire well.

Check for water in the spare tire well too. Sorry, just noticed the post above mine.

So I was completely unable to lift the carpet edges, but near the mats in the front, the floor felt cold. I couldn’t tell, however, if that was simply moisture off my shoes, water coming in or just cold.

I also checked the trunk and as of this afternoon (when the car wasn’t fogging) there was no water and the carpeting felt perfectly dry. I’ll check again when it fogs up though.

Thanks for the help!

You will probably have to remove some plastic trim to lift the carpet edges. There is water somewhere. You have to find out where it is and how it got there.

Easier said than done, I know, because I’ve been in your position. Do whatever it takes to get under the carpet. I’ll bet you will find soaked padding somewhere.