Why are my car windows icing over... on the inside??
December 5, 2018 6:14 AM   Subscribe

On cold mornings, when I leave for work, my car windows often have the usual rime of frost on the outside... but my rear window is often completely iced over on the inside. I have never had this happen before! What could be causing it?

There is no sign of any moisture leaking into the car -- nothing has spilled, no wet umbrellas, no leaks around the doors or windows. It also never happened before we moved into our current home -- maybe the sun is hitting it differently than before? Any ideas on how I can make it stop happening? Scraping the interior of the window isn't terribly easy to do!
posted by sarcasticah to Home & Garden (15 answers total) 4 users marked this as a favorite
Solution: If you leave a window open a crack, it will allow any moisture to escape (or for the air in the car to match the outside humidity). Alternatively, open the windows or doors wide for a few minutes when you get home and allow the moist air to escape.

Cause: More debatable, but there is a source for moisture being sealed inside the car, likely from you the driver. Could be due to many things: the length of your commute changing; your heater setting increasing; you're carrying a passenger you weren't before that brings in more humidity....
posted by cardboard at 6:19 AM on December 5, 2018 [2 favorites]

I had the same problem with one of my other cars; lots of snow/slush had accumulated in the boot trays and the humidity got into the air, and just seemed to stay there.

I found a very helpful trick -- bought 2 pairs of those cheap knee-high pantyhose socks, and filled two of them with silicone cat litter. Tied it with a knot, then slipped the extra one over it and tied that in a knot.

I would leave one near my front dash and one in the back cargo area (it was a wagon), and they would both absorb extra humidity all winter long! An inexpensive DIY solution that worked really well for me...
posted by Jade Dragon at 6:52 AM on December 5, 2018 [18 favorites]

Some DampRid or something like the Eva-Dry dehumidifier back there should help remove the interior moisture. Also, this is probably obvious, but if the car has a rear window defroster it will help as well.
posted by exogenous at 6:53 AM on December 5, 2018

My commute to work is much, much shorter than it was before we moved -- all of five minutes at most, instead of the 20 minutes or so it was. It happens a lot on days when it's completely dry out, and I haven't tracked any snow or slush into the car on my shoes. It's very odd. I'm going to try the cat-litter trick, though, and see if that helps. (The rear window does have a defroster, but it takes forever to clear the frost on the inside.)
posted by sarcasticah at 7:20 AM on December 5, 2018

Is it possible you're turning the heater on less and thus losing its drying effect?
posted by trig at 7:30 AM on December 5, 2018 [4 favorites]

I think trig has the right idea. If your commute is 5 minutes, it seems likely you get less than 1 minute of actual heat coming from your car. I imagine you continue to breath throughout the ride, though, and your breath will have quite a lot of moisture in it, even if the air is dry that day.
posted by Phredward at 7:41 AM on December 5, 2018

If you wind up going to the store anyway, they sell hanging Damp-Rid packages for use in closets. This may be easier to deal with (and lower risk of spillage) than the usual tubs it comes in.
posted by Huffy Puffy at 8:07 AM on December 5, 2018 [1 favorite]

It is possible that a small amount of water is sitting in the car somewhere - under the carpets or inside a door, or inside the spare wheel well etc. It doesn't take much. Things to check (although the short commute is my suspicion as the issue)

Sunroof (if you have one) not draining.
if you run water around the sunroof it should run out the bottom of the car eventually. If it isn't then the drain hose may be allowing water into the car somewhere and it is sitting. You can run a piece of electrical wire down them and clean them out if necessary. Or a little bit of compressed air.

Door drain holes blocked.
Open the doors and along the bottom edge should be small openings to allow the water that runs down the outside of the windows to come out the bottom of the door. A small piece of wire ( paperclip maybe?) can be used to just poke around in those holes and check they are not full of gunk.

Boot (trunk) floor drains blocked
There should be some little rubber bungs in there that allow any water to drain out. Check they are clean and not filled up with dust/debris and blocking the drain holes.
posted by Brockles at 8:20 AM on December 5, 2018 [3 favorites]

Seconding Brockles. This happened in my hatchback. It turned out to be a slow leak in the trunk area through a poorly seated seal. My spare tire well was flooded with water, and I didn't realize because it was beneath the trunk liner. Nothing in the car seemed wet except the ice on the insides of the windows.
posted by a moisturizing whip at 8:45 AM on December 5, 2018 [3 favorites]

If it's iced up when you enter the car cold, moisture from your breath is immaterial. This is most certainly being caused by extra moisture in the car's interior environment. Small leak in the trunk or at the rear window would be likely culprits and easy to overlook.
posted by humboldt32 at 10:04 AM on December 5, 2018

Came here to say exactly what Brockles and a moisturizing whip said. And if you happen to have a Honda Fit, memail me and I can send you the links to the known issues re: the hatch.
posted by pixiecrinkle at 10:25 AM on December 5, 2018

Does your car have air recirculation? you want that turned off
posted by canoehead at 10:52 AM on December 5, 2018

How useful! I've begun having this same interior ice/moisture on my windshield in my old Kia (2005). I'll check all those drain holes after the snowmageddon that's about to hit us. And I may get that Damp-Rid. Thanks.
posted by MovableBookLady at 12:04 PM on December 5, 2018

I had this problem allllllll the time, and the solution was to always leave my car’s AC/fan open for fresh air instead of using the recirculate setting.
posted by Andrhia at 5:49 AM on December 7, 2018

So, a week later, I can update to say the Damp Rid has helped a lot! I checked the car, the trunk, etc., and there was no water sitting anywhere, and no damp spots. I bought obe of the Damp Rid bags that you put in a closet, and chucked it onto the shelf under the back window, and presto, the ice has not come back. thanks, all!
posted by sarcasticah at 7:54 AM on December 10, 2018

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