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What options are there to keep the windshield more or less ice-free during extreme cold (-30 degrees) without using the heater of the car?

We are currently on a road trip through the Baltic states and car heater broke. It is blowing only cold air. The motor temperature is okay (around 85 degrees) and the cooling liquid is filled up, has no air bubbles and heat is transmitted through the pipes going from the cooling unit. According to the only car mechanic we could find, the problem is deeply hidden in the car (the valve that mixes warm and cold air is probably broken), so it would take long to fix it.

We have however only limited time and need to be back in Russia in 2 days. Driving with warm clothing and stoping for coffee frequently etc is alright, but since the windshield fogs up and the interior's moisture freezes from the inside, it is impossible to see anything and therefore also impossible to drive the distance to the next bigger town (about 160km).

We have tried de-icing spray (alcohol-based), which of course quickly evaporates and leaves a thin layer of water which...freezes. Leaving the (cold) fan on blows dry air over the windshield and very slowly creates a spot that is cleared. As it seems, our best bet would be a portable car heater that runs on 12V. Those seem to be sold out in the town we are staying at the moment. We are hoping to drive to Tartu, which should be large enough to have such a 12V car heater in stock.

What other options are there to temporarily de-ice the windshield from the inside?

In case it matters: the car is an Opel Corsa from 2008, using gasoline as fuel.

  • Before driving we scratched ice off the windshield and wiped the inside dry with paper towels. Then we started driving with the vent blowing over the windshield. We also left one of the back windows a bit open to let moist air escape. On our 5 hour drive, only towards the end it got difficult to see the road and iced up quickly each time after wiping the windows again. In total we had to wipe them about 4 times. During the 2 hours we stood at the border crossing, we left the car and rolled down the windows (earning strange looks from other drivers ^^). – ahemmetter Jan 9 '17 at 6:26
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The absolute easiest way to keep the windshield clear is to drive with the window open. This will remove the humidity from the car very quickly. FYI, the humidity comes from your breath, so opening the window periodically should work.

The only problem is that it might be brutally cold. So maybe instead you can find a way to direct the airflow by cracking the driver's window diagonally across the car to the rear passenger side window. Maybe 3 cm on both sides? Give it a try. I did this in an old Pontiac during the 80s; kept the car form being too cold, while keeping the humidity down.

Best part of this option: it is free, if your windows still function.

Edit for Safety:

I wanted to add this comment, related to safety, to this, courtesy @ZachMierzejewski. As he said:

This only works if you do this immediately after getting in the car. If I drive for 5 minutes with the windows closed and the windshield starts to fog/ice on the inside, opening the window won't make the fog/ice go away. This can really suck if you're 5 minutes into your drive and you can't pull over; I know from personal experience. Keep a roll of paper towels in your car within easy reach as a backup. You can wipe away the fog/ice. This is more dangerous than preventing the fog/ice in the first place, but less dangerous than driving with a foggy windshield. –

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    This only works if you do this immediately after getting in the car. If I drive for 5 minutes with the windows closed and the windshield starts to fog/ice on the inside, opening the window won't make the fog/ice go away. This can really suck if you're 5 minutes into your drive and you can't pull over; I know from personal experience. Keep a roll of paper towels in your car within easy reach as a backup. You can wipe away the fog/ice. This is more dangerous than preventing the fog/ice in the first place, but less dangerous than driving with a foggy windshield. – Zach Mierzejewski Jan 8 '17 at 16:11
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Does the air conditioner work? If so, you can blow COLD and DRY air onto the windshield from inside by setting the controls to: A/C, WINDSHIELD, OUTSIDE AIR.

The cold/dry/outside air from the A/C will prevent the warm/most/inside air from you from getting to the windshield and condensing/freezing.

Even if you don't have A/C, you can try with just cold/outside air.

  • If the problem is moisture in the inside air, would a dessicant-based dehumidifier work? I'm thinking of the ones that use bags of crystals or a hygroscopic brick, such as this: amazon.co.uk/Unibond-Humidity-Absorber-Device-Stand-alone/dp/…. – Roger Lipscombe Jan 8 '17 at 9:55
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    The A/C compressor usually turns off in the 2–5°C range, so that probably won’t work at -30°C. – user149408 Jan 8 '17 at 13:50
  • @RogerLipscombe Wow, I just ran the numbers: 300g dessicant, (1/2) * 900ml / 24hrs = 18.8g of H2O output by a human in a half hour, 0 degrees C, 60%RH and, theoretically, it should be able to absorb all of the moisture produced by a human. But in the real world, you wouldn't be able to direct all your moisture at the device so some would still drift to the windshield and freeze. Also, this doesn't take into account outside air being blown in through the vents. Summary: It might help, but is not a solution. – Zach Mierzejewski Jan 8 '17 at 16:29
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The easiest thing you could use right now is a de-fogging agent. Anything which will keep the humidity off of the windshield. What I'm talking about is something like Rain-X. At least this should keep the inside from getting frosted over. Wipers are about the only thing on the outside which is going to work.

If you are wondering, the physics behind it are thus ... right now without the windshield treated, the humidity in the air collects on the windshield because the windshield is colder than the ambient air inside the vehicle (your breath and body heat make this so). The fog collects on the windshield because of the dew point. To prevent this, you apply the Rain-X (or whatever you can get your hands on) to the inside of the windshield. This puts a coating on it which is superhydrophobic or otherwise keeps the water from whetting glass surface (the water would bead on top of instead of coating the surface ... if enough water can form on the surface). Without being able to whet the surface of the glass, it should stay clear for the most part.

PS: Although very hard to do right now, getting the inside of the windshield as clean as you can get it before applying any treatment will help tremendously as well.

  • We will check some gas stations soon for this de-fogging agent and use it is not combination with the de-froster setting on the car on cold – ahemmetter Jan 8 '17 at 6:24
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Another thing that you might have luck with is to run the fan at low speed with the defroster on (assuming you can control the airflow). That will keep air moving over the windscreen and will help both to evaporate moisture and to prevent the windscreen from getting (too much) colder than the rest of the car.

You might also try looking for some of the chemical hand or foot warmers, they might help you get some heat onto the windscreen.

  • Yes, the air flow can be controlled. The day before we drove about 90km by having the defroster running (in the hope it would suddenly jump back to life) and ice was not such an issue. Today it was even colder though and the dry air didn't seem to help anything. But probably we didn't try it long enough. – ahemmetter Jan 7 '17 at 20:33
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    Wonder if you could heat up something like a bag of sand (kitty litter?) in the engine compartment? If you had two or three of them perhaps you cold get them hot and then put one on the glare shield to warm the air. Trade them out as they get cold. – dlu Jan 8 '17 at 10:09
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Clean your windshield with a special sponge (most bigger gas stations should have those). Apart from removing dust particles from your windshield (which contribute to fog buildup), they are also treated with something that will further prevent the windshield from building up.

If you can’t find any of those, you can make a substitute at home: pour liquid soap onto a dry (or slightly moist) sponge, and let it soak.

Additionally, run the fan in defrost mode (directing the air flow to the windshield) at high speed. This will cirulate dry air (from outside) past the windshield and carry away some of the moisture.

If you can get anything that’s warm (but dry) and place it in the airflow, that would also help. I’m told that back in the days of the VW Beetle, owners would heat bricks in the oven at home and place it in the footwell of their cars before going on a trip in winter.

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