by Lori Straus

Windshield washer fluid is not a one-size-fits-all situation. Your car, where you live, and what season it is will all dictate what kind of windshield washer fluid you need.

What Is Windshield Washer Fluid?

Basically, windshield washer fluid comes in two basic formulas, depending on the season: bug season and frost season. In common parlance, that’s summer and winter. It’s up to you when you want to transition between the two types of fluid in the spring and fall.

The main difference between both types of fluid is what it actually removes. Windshield washer fluid for colder months helps break down ice and frost that collect on your windshield. It’s a mixture of water and antifreeze, usually methanol. (Other possible alcohols are ethanol and isopropyl alcohol.)

By contrast, windshield washer fluid for the warmer months helps breakdown dirt, grime, and even bugs that smash onto your windshield as you drive. It’s generally a mix of water, detergent, and often a few other ingredients.

Windshield Washer Fluid for the Winter

Generally, the more methanol (or other alcohol) is mixed in with water, the lower the freezing point of the solution. Common sense would suggest that mixing enough alcohol with water will mean that you will never have an ice problem on your windshield. However, we all know that isn’t true. Why?

Methanol is highly flammable. So, filling your windshield washer fluid reservoir with a highly flammable liquid is not exactly a smart idea. Plus, methanol can damage your car’s paint, rubber, and other components.

When you buy windshield washer fluid, the colder the temperature on the bottle, the more alcohol there is in the solution. However, you’ll never be able to rid your windshield of all ice all the time.

Why Antifreeze Doesn’t Always Melt Ice Immediately

We’ve all been there: it’s -20˚C outside, you’re late for work, and your windshield is completely frosted over. You blast the defroster, but because your car’s engine is cold, nothing changes right away. (You’ll actually need to drive your car to fully warm up the engine. Letting it run for more than a few minutes does nothing but waste gas.) You sit in your frigid car and start pumping the windshield washer fluid, only to swear at it, because the ice on your windshield isn’t dissolving fast enough.

That’s because as you spray, much of the methanol can evaporate and be carried off in the wind, leaving only water behind. The temperature rating on your fluid container actually pertains to the fluid not freezing up in the reservoir up to that temperature.

Our only advice on mornings like this is to get out the scraper: you are legally required (and should do so out of common sense) to have a fully cleared windshield. No driving with a tiny frost-free hole scraped out for you to peek through.

Read the Label to Buy the Kind That’s Right for You

Read the label on the container and make sure that the fluid fits your needs. When the seasons change and you change your fluid, be sure to empty the reservoir. (Just keep spraying until nothing more comes out.) Windshield washer fluid lets us keep our windshield clean while we’re driving, but it can give you a headache if you have the wrong type for the season. Spend a few minutes reading bottles, maybe even check the odd online review, and buy the one that’s best suited for you.