How do I know? Well, let me lay out a scenario for you; you’re in bumper to bumper traffic with cars rolling a few feet before coming to a complete stop, the SUV ahead of you decides to clean its windshield using the windshield washer jets at the base of the windshield. And voila, a good portion spray leaps over the SUV and lands on your hood and windshield. They need to have those jets adjusted, but other than that no big deal, right? Or is it? It turns out it is a big deal, and there’s two reasons why. First, your hood covers the vehicle’s engine which is most likely an internal combustion engine. No matter whether it’s a pretol or diesel it still generates wait for it….heat. The longer the car runs it will keep the temperature of the hood warmer than the ambient air temperature. Think of it like this, you wouldn’t wash your car in the midday sun, right? The sun heats up the car (Well above 100 degrees), turning your vehicle’s painted surfaces into a griddle that will roast any small animal or vaporize any fluid placed on it in short order. After your car’s been running or when the ambient temperature is warm the surface of your car continues to be able to heat any fluid that lands on it causing it evaporate leaving behind mineral deposits in the paint also known as water etching. If it’s not dealt with quickly to remove it, it can lead to some minor damage. Instant frowny face, do not pass go. You’ve now just earned yourself a paint-correction session the next time your car gets detailed. The second and more important reason that it’s bad for your car relates to the ingredients used in wiper fluid cocktail. That blue color does not denote wholesomeness or purity.
The ingredients that “generally” make up this ever blue and never freezing cocktail are generally water, methyl alcohol, and sometimes even some ethylene glycol. Strange bedfellows. Alcohol usually accounts for 30-50% of the mixture. Now water is good, but it doesn’t have the bug busting or freeze prevention properties that alcohol added can provide. What’s important to note is that alcohol is NOT good for painted surfaces. Why is that you ask? Methanol is toxic to humans, it’s not the drinking kind. Methanol is used in laboratories as fuel or solvent. The chemical definition of a solvent is: able to dissolve other substances. Wait, what?? So much so that windshield wiper fluid has it’s own Data Safety Sheet detailing hazards, handling instructions, and emergency procedures for various interactions with the liquid outside of it’s designed home: the fluid reservoir in your vehicle. You can check out a generic data safety sheet from BP HERE. Now you’re a smart cookie and recall the part where I mentioned that the cocktail also contains water. So you think the alcohol’s diluted so it won’t harm your vehicle’s paint, nothing to worry about! Please see reason #1.
In general these fluids are made to be used in automotive applications, but that’s in the context of the design to keep the fluid on the glass quickly removed by the wiper blades. Generally when you are most likely to use the wiper washers are in the winter months to remove the crust of salt and snow scum from the windshield. You’re probably ok then. When you have drops land on your hood on a warm day or hot hood, you may need to treat the area as soon as is practical. I keep a detail kit in my car almost all the time with several goodies, and always with two essentials; microfiber towels, and a spray bottle filled with H2O. I can’t tell you the number of times I’ve parked outside only to return and discover the fowlest transgression had befallen my pride and joy. No worries! Before it had time to etch into the paint I used the spray bottle and microfiber towels to remove bird droppings. And it will work to dilute almost any fluid that may come in contact with the painted surfaces of the car. Remember back the scenario at the start of this article when the motorist sprayed my car in traffic with wiper fluid, I didn’t have the ability to use my detailing kit to remove the fluid, and had to wait until parked to pour distilled water over the surface of the affected areas. Everything turned out ok, but if I had driven longer or not rinsed the surface of the hood with water there’s a good chance I’d have earned some water etching marks.
In closing wiper fluid comes in a variety of formulas so there can be no absolute answer about whether it will or won’t fade paint. We do know that it will most likely contain a solvent, which we know can fade paint. If you want peace of mind for your vehicle you should research for brands that provide proof that their product will not damage the painted finishes and rubber trim pieces of your vehicle. And for those times when you receive an unexpected dose from a fellow motorist just use water and microfiber to remove it from the painted surfaces. Either way it won’t consume the paint on your car before your eyes, but if left untreated it could diminish the quality of your vehicle’s finish leaving spots of water etching or other imperfections in the paint or deteriorated rubber trim/seals.