# Car windows misting / icing up inside. Any fix? **URL:** \ **Category:** Factual Questions\ **Created:** [January 19, 2003, 10:07pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689 "2003-01-19T22:07:45Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![ianzin](https://avatars.discourse-cdn.com/v4/letter/i/ed655f/32.png) [@ianzin](https://boards.straightdope.com/u/ianzin)\ **Post date:** [January 19, 2003, 10:07pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/1 "2003-01-19T22:07:45Z")
I have a moderately good second-hand car (Toyota) which seems to function normally in all respects. The only problem is that in cold or damp weather, there’s a lot of condensation on the _insides_ of the windows. In very cold weather (such as the snowy Winter weather we’ve had recently here in England) I’ve even had _ice_ form on the insides of the windows. Q1. Is this as abnormal and strange as I think it is? Or does it happen to many of you as well? Q2. How do I stop it happening? The only thought I’ve had is that the car _is_ supposed to be hermetically sealed, or close to, but there’s a fault somewhere e.g. one of the rubber mouldings around one window must be faulty or broken. But I’ve looked closely and I can’t find any trace of such a flaw. As I said, the car itself is only 3-4 years old and is in pretty good condition. Please help if you can. ---
**Author:** ![barbitu8](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@barbitu8](https://boards.straightdope.com/u/barbitu8)\ **Post date:** [January 19, 2003, 10:13pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/2 "2003-01-19T22:13:49Z")
Try running your AC with the defogger and heat on high. Works for me when the inside fogs up. ---
**Author:** ![Finagle](https://avatars.discourse-cdn.com/v4/letter/f/b19c9b/32.png) [@Finagle](https://boards.straightdope.com/u/Finagle)\ **Post date:** [January 19, 2003, 10:51pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/3 "2003-01-19T22:51:49Z")
Are you leaving anything in your car that might be emitting moisture? Even the snow from your boots melting on the car carpet has to go somewhere. So when the car heats up during the day, you get a lot of water vapor and that then condenses on the windows and freezes. ---
**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\ **Post date:** [January 19, 2003, 10:53pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/4 "2003-01-19T22:53:05Z")
Is this happening to anyone else’s car near by? That’s the only way to tell if it should be happening or not. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [January 19, 2003, 11:11pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/5 "2003-01-19T23:11:43Z")
Cars are not supposed to be completely sealed. Supposedly the old volkswagon beetles were, which is why they suppesedly flaoted too. The one time I watched someone try it, it sank. I second the suggestion of turning on the AC with the heater on. This works remarkably well on some cars. I’ve known quite a few cars that like to mist up in cold and damp weather, and this almost always fixes the problem. The only case where I can think of that there might be something wrong with the car is that if the “water” feels a little oily or is difficult to wipe off. If this is the case, then it might not be water that is misting up your car, but engine coolant that is leaking in through a leak somewhere (most likely the heater core). Do you have to fill up the coolant periodically or is it staying at a normal level? ---
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [January 19, 2003, 11:15pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/6 "2003-01-19T23:15:43Z")
That shouldn’t happen. It happened to me with an old car because of a leak. Check around for damp spots, on the floor, in the trunk, also in the sunroof, if it has one. One thing that might help in the short run is to get the heat going full blast and open up the windows to vent the humid air. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [January 19, 2003, 11:48pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/7 "2003-01-19T23:48:26Z")
First off don’t use the recirculation feature on the heater when it is cold/damp outside. The air inside the car is more humid than the air outside (due to you exhaling water vapor and any water/snow that may have entered with you on your shoes or clothes. Using recirc will keep this warm humid air inside the car where it will condense on the inside of the glass. A/C is a dehumidification process so using the A/C will remove a lot of moisture very quickly. Many newer cars with climate control systems default to A/C, and no recirc when defrost is selected. If the inside of the glass of your car has any dirt of deposits on it, condensation will more easily form than if the glass is clean. It’s a pain in the butt, but clean the inside of all the windows and you may see a vast difference. ---
**Author:** ![SandWriter](https://avatars.discourse-cdn.com/v4/letter/s/8491ac/32.png) [@SandWriter](https://boards.straightdope.com/u/SandWriter)\ **Post date:** [January 20, 2003, 12:19am UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/8 "2003-01-20T00:19:02Z")
What? If you are talking about when you walk up to the car after it has sat all night and there is moisture on the windows, then something is wrong. I agree with Finagle and Cheesesteak, there is water in the car either a leak or something you are putting in there. Can you see any mushrooms? If you suspect a leak, don’t rule out the bottom of the car. If it is rusted out, then water can be spraying/splashing up from the road, soaking the carpets, then evaporating. If you are saying that you are driving along and the windows start to fog up, then you have another problem, poor ventilation. TOT,IRL, I was delivering pizzas and my car would fog up on the inside, especially when it was raining. The only thing that worked was to have the tempurature set to high heat and have the fan on high and direct the air through defroster. I also had to have all the windows rolled down a 1/4 of an inch to allow the moisture to escape. The car didn’t have a rear defroster, so if I didn’t use the above procedure the rear window would get all fogged up. Good Luck ---
**Author:** ![ianzin](https://avatars.discourse-cdn.com/v4/letter/i/ed655f/32.png) [@ianzin](https://boards.straightdope.com/u/ianzin)\ **Post date:** [January 20, 2003, 1:09am UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/9 "2003-01-20T01:09:19Z")
Thanks all for suggestions so far. Seems some clarification is warranted. 1. I’m aware that, once I’m in the car, I can clear the windows using the heater and AC. That’s not really what I’m asking about. I’m trying to prevent it happening in the first place. 2. Yes, **Sandwriter** , I’m talking about going to the car after it’s been parked on the street at night during cold, damp weather, and finding way more condensation on the insides of the windows than I think is right or normal. There’s no problem once I’m actually driving along. No mushrooms or obvious trace of leak or seepage, though. 3. No, **Finagle** , nothing gets left in the car. Nothing. The crime rate round here is too high. The car is EMPTY. 4. Good point, **X Ray Vision**. Yes, I sometimes find my car windows all misted up or iced up and cars parked fore and aft seem unaffected, or affected a lot less. And these other cars may be roughly the same general age/condition as mine or even a lot crummier. So it’s not just that I’ve got a crappier car. 5. **Engineer comp geek** may be on to something. I have noticed that when I try to wipe down the inside of the front windscreen (windshield) the moisture seems slightly oily and harder to wipe away than pure water moisture or condensation on its own ought to be. However, the engine coolant doesn’t seem to be leaking. The whole engine is in good condition, and the coolant level doesn’t seem to be leaking or need topping up more often than any other car I’ve known. Also, I have difficulty understanding how the engine coolant could be condesing on the insides of the windows. But then I can be pretty ignorant in such matters. 6. Good point, **Rick**. My car’s AC has 2 options - recirculate or exchange (with outside). I’ll try your idea and see if it makes a difference. ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [January 20, 2003, 4:47pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/10 "2003-01-20T16:47:54Z")
Im in California, so no ice, but if the window is left open or there is water on something, then yes, misting. At the auto parts store you can get something like FogX to keep your windows clear. it works great for me. ---
**Author:** ![drpepper](https://avatars.discourse-cdn.com/v4/letter/d/8baadc/32.png) [@drpepper](https://boards.straightdope.com/u/drpepper)\ **Post date:** [January 20, 2003, 7:18pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/11 "2003-01-20T19:18:11Z")
To further add to **Engineer** ’s theory, I heard a very similar scenario asked on ‘Car Talk’ a couple weeks back. Once Click and Clack determined that it was a fairly aggressive condition and an ‘oily’ type consistency, they groaned and told the caller that it was a serious problem and the moisture itself was (coolant? antifreeze? I can’t remember-- Some engine fluid of some sort), and that it was difficult/expensive to fix. That’s all I remember about the call. ---
**Author:** ![dauerbach](https://avatars.discourse-cdn.com/v4/letter/d/c2a13f/32.png) [@dauerbach](https://boards.straightdope.com/u/dauerbach)\ **Post date:** [January 20, 2003, 7:24pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/12 "2003-01-20T19:24:53Z")
Yeah, if the “moisture” has an oily consitancy it means you have a leak from your heater core. If you think about it, even a tiny leak would cause an abnormally high humidity in the small sealed volume of a car. Try putting some of that “leak stop” radiator stuff in and see what happens. Also check the passenger side floor to see if it is a little damp. ---
**Author:** ![Tuco](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tuco](https://boards.straightdope.com/u/Tuco)\ **Post date:** [January 20, 2003, 7:25pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/13 "2003-01-20T19:25:28Z")
Could be a small leak in the heater matrix, that would explain how coolant would get on the windscreen. Does your car use a lot of water? ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [January 20, 2003, 9:33pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/14 "2003-01-20T21:33:09Z")
It wouldn`t have to loose a lot of coolant for the windows to get fogged up. It may be a pinhole in the heater core. Or a loose hose clamp on the input hose through the firewall. In any case it is definitely antifreeze on your windows. When you drive around with the heater on you may notice a sort of sweet smell in the air due to the antifreeze being blown about. ---
**Author:** ![GOM](https://avatars.discourse-cdn.com/v4/letter/g/5f9b8f/32.png) [@GOM](https://boards.straightdope.com/u/GOM)\ **Post date:** [January 21, 2003, 1:21am UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/15 "2003-01-21T01:21:16Z")
> [@](#): > > \*Originally posted by dauerbach \* > \*\*Yeah, if the “moisture” has an oily consitancy it means you have a leak from your heater core. If you think about it, even a tiny leak would cause an abnormally high humidity in the small sealed volume of a car. Try putting some of that “leak stop” radiator stuff in and see what happens. Also check the passenger side floor to see if it is a little damp. \*\* With those symptoms, it is most likely your heater core. Antifreeze is very slippery, sticky stuff. The heater core is located, on many cars, under the right hand side of the dashboard next to the firewall. The suggested “stop leak” cure might take care of the problem. OTOH, stop leak could also clog up your radiator and cause you worse problems. The correct fix is to have the heater core replaced. I’ve had to have it done on a couple cars. Replacing the core solved the problem both times. Btw, how often do you change your antifreeze? You mention that the car is 3-4 years old. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [January 21, 2003, 4:24am UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/16 "2003-01-21T04:24:49Z")
> [@](#): > > \*Originally posted by ianzin \* > \*\*6. Good point, **Rick**. My car’s AC has 2 options - recirculate or exchange (with outside). I’ll try your idea and see if it makes a difference. \*\* I’d bet dollars to donuts–since it appears you’ve been using recirc–that’s the problem. Check your manual. It probably says that you should use recirc only to speed up the warmup process, and you should turn it off after that. People often assume that it makes the car warmer, and saves energy–so they use it all the time. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [January 21, 2003, 4:54am UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/17 "2003-01-21T04:54:44Z")
Do **NOT** use “recirc” for any heat, defrost, or vent functions. The **ONLY** time to use “recirc” is for the coldest air conditioning. ---
**Author:** ![mrcrow](https://avatars.discourse-cdn.com/v4/letter/m/838e76/32.png) [@mrcrow](https://boards.straightdope.com/u/mrcrow)\ **Post date:** [January 21, 2003, 11:51am UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/18 "2003-01-21T11:51:15Z")
there is water getting in somehow and not getting out so you heat it up and then it condenses overnight i had this with a cortina and after some really extensive inspection discovered a small hole in the roof guttering…it was an old model that may not be your problem but i feel there is an inlet somewhere that is causing the moisture to collect good luck with the exercise windscreen leaks are a nuisance as well… 🙂 ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [January 21, 2003, 1:22pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/19 "2003-01-21T13:22:00Z")
Put a cantainer of stop leak (brand name Bars) in the radiator and follow the instructions. If you have a small leak this will fix it for now. If the leak comes back then you should consider replacement or repair. The stop leak stuff will not clog your radiator or heater core, it actually conditions and prevents corrosion. It reacts with the air at the leak and hardens at that location to seal the defect. I`ve replaced several heater cores on my various vehicles and in some cases it can be very difficult. Some cars require partial dismantle of the dash board and others can be removed easily through the fire wall. The hardest one for me was an 88 thunderbird, took about 6 hours. Easiest were the Chevelle and the Bronco, they could both be done in the parking lot of the parts supply store. ---
**Author:** ![Sebhal](https://avatars.discourse-cdn.com/v4/letter/s/47e85d/32.png) [@Sebhal](https://boards.straightdope.com/u/Sebhal)\ **Post date:** [January 21, 2003, 1:31pm UTC](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689/20 "2003-01-21T13:31:29Z")
I know that in that cold snap my windscreen iced up on the inside after I got into the car, all that moisture caused by breathing out. I avoided it by leaving the window open until the engine had warmed up, then close the window and turn on the AC to keep it clear. N. [Next page](https://boards.straightdope.com/t/car-windows-misting-icing-up-inside-any-fix/149689.md?page=2)