Our fathers and grandfathers liked to pour methylated spirits into the windscreen washer system in winter. If the contents weren’t used up during the periods of frost, the mixture would still be sloshing around in the container in the summer. And that’s the only additive the water then got. People still do this today, though more rarely; but this behavior is false economy. And you can’t even call it that because methylated spirits are not exactly cheap. The thing that keeps most drivers from using methylated spirits is the pungent smell that also tends to make its way into the car through the ventilation system. By now there is even a whole variety of fragrances on offer for delicate noses.

But a good additive needs to do more than just smell good. Especially in summer it needs to clean well. That’s more than either pure water or wonderful methylated spirits can handle. Particularly now that mosquitoes and other insects often get squashed on windscreens and headlights, cleaning them is hard work for the washer systems and wipers.

But are there good and bad additives? Aren’t they all the same? That’s like asking whether all tires or even cars are the same, not to mention car lights. Speaking of lights – what does the windscreen washer system have to do with them?

Let’s take one thing at a time. As for all products, there are huge differences in quality when it comes to additives for water. Poor-quality products will produce streaks for example, or they foam heavily which could blur your vision for a short time. Foaming particularly occurs in newer cars which are equipped with fan nozzles. But certainly not all additives can deal with these nozzles, therefore the better ones say so on the pack.

Headlight covers and windscreen wipers are sometimes allergic to poor-quality additives.


It also includes information on whether the product is suitable for polycarbonate covers. And that leads us to lights. All cars with xenon lights (except the ones with rare 25-watt systems) have a headlight washer system (HWS). Stronger LED headlights also need to have one, and halogen ones are sometimes also equipped with one. Today virtually all headlights have covers made of polycarbonate. At a pressure of around 100 bar, the HWS “fires” the water onto the plastic treated with a thin clear coating. It’s not too difficult to imagine what damage too aggressive chemicals could cause.

Matt, opaque or discolored surfaces are often the result of unsuitable additives. This also affects the light because it compromises the optical characteristics. Normally covers can’t be replaced individually, and a new headlight unit costs several hundred euros. A better additive is considerably cheaper. That also applies if your car doesn’t have a headlight washer system; the rubber of the windscreen wipers doesn’t like products that are too strong either.

You can’t go wrong with products from well-known brands, especially if it specifically says on the packaging that they’re suitable for fan nozzles and polycarbonate. Accurate dosage is also beneficial. We often put too much in the water, which doesn’t increase the effect – quite the opposite.

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