My wiper fluid freezes. What am I doing wrong?

January 13, 2016 8:53 AM

Yesterday it was -6°C in Montreal. I used the windshield spritzers to spray wiper fluid on my windshield. The thin layer of fluid immediately froze, rendering the windshield opaque until I could get it warmed up with the defroster. This happens regularly. It even happens after the windshield is clear of ice. I'm using regular windshield wiper fluid that' supposed to be good down to -40°. Am I doing something wrong, or is -40 a huge fib?
posted by musofire to Travel & Transportation (9 answers total)

I'm assuming you are not mixing water with the washer fluid ? (or have in the past). Takes some water (more than a little) to raise the freezing tem.

Are you driving at the time, or sitting in the driveway/traffic when you spray the fluid ? If you're driving, the air passing over the windshield can quickly make the fluid freeze, even if the ambient air temp is above the freeze point.
posted by k5.user at 8:57 AM on January 13, 2016

I've noticed this too. I think the alcohol in the washer fluid is evaporating quickly when you spray letting it freeze at warmer temps. Keeping my defroster on helps a lot with this problem.
posted by samhyland at 8:59 AM on January 13, 2016

The -40ºC rating is to let you know it won't freeze-up in your reservoir or lines below that temperature. I haven't thought about what the physical mechanism is, but the freezing on the windshield is normal behaviour until the car warms up.
posted by cardboard at 9:02 AM on January 13, 2016 [5 favorites]

All washer fluid will freeze when it disperses on the windshield, the -40c just means you won't have a fluid reservoir full of ice.
posted by Cosine at 9:04 AM on January 13, 2016 [4 favorites]

At truck stops and such, you can buy nearly pure isopropyl alcohol. Just add a quart or so for each gallon of washer fluid. Or cheap vodka, which is what they do in Russia.
posted by beagle at 9:42 AM on January 13, 2016

Yes, the problem is that the alcohol, which lowers the freezing temperature, evaporates first, leaving water behind - which freezes. The only solution I know is to wait until the windshield is warmed up.
posted by mr vino at 9:49 AM on January 13, 2016

Best answer: Go to your local Big Box store and get two things:

1. 70% (not 50%) isopropyl (not ethanol - check the label) alcohol 2. Deicing spray

Get rid of whatever is in your windshield washer well now. Pour in a MIX of half of that alcohol and half water (you need the water) - that stuff will actually work . Most of the -40 below hype is crap when it comes to commercial products.

The deicing spray is amazing stuff - expensive so use it only when you need to GO NOW. I used it yesterday on a 17 degree day with all my windows frosted and very slightly snowy. Everything defrosted in about 30 seconds and stayed that way while I drove and the defroster warmed up. It probably cost me a 75 cents but was worth it to get to my job interview.
posted by AGameOfMoans at 10:02 AM on January 13, 2016 [4 favorites]

The -40ºC rating is to let you know it won't freeze-up in your reservoir or lines below that temperature.

Way after the edit-window, I meant above that temperature.
posted by cardboard at 11:19 AM on January 13, 2016

There are two things going on here.

First, if you have the same washer fluid from last summer, some of the alcohol may have evaporated from the reservoir, leaving behind a more watery fluid. This is the same process as a distillery in which the alcohol evaporates leaving water behind. Your -40 fluid might have started out that way, but it might not be -40 anymore.

Second is that an alcohol mixture evaporates more quickly than water because it has a higher vapor pressure. This means that when you spray it on your windshield it starts to evaporate and cools the windshield, just like dabbing rubbing alcohol on your skin. This is especially the case if you are moving at highway speeds and the wind is blowing across the surface. So your windshield is going to be significantly colder than the outside air temperature due to evaporation.

So the the answers are to make sure you have fresh fluid when entering the winter driving season, or to spike your fluid with extra alcohol. However you want to be careful not to have more than about 50% alcohol to prevent damage to the finish of the car.
posted by JackFlash at 2:14 PM on January 13, 2016