Nowadays, antifreeze for windshield washer systems is even available from discount chains, but the quality of the products on offer varies enormously. This becomes particularly evident when the same reservoir is used for headlamp cleaning as well. Although the windshield is immediately in front of the driver – and any unsuitable additives cause smears that impair his or her vision – the problems related to headlamp cleaning are of a different nature. For use with headlamp washer systems, the antifreeze and other additives (or indeed the water itself) must be of a suitably high quality.

With very few exceptions, today’s headlamp lenses (formerly also known as diffusers) are made of a thermoplastic material called polycarbonate. When exposed to particular chemicals, this material exhibits a stronger allergic reaction than windshield glass does. This sensitivity is compounded by that fact that headlamp water jets actually hit the protective coating on the headlamp lens rather than the polycarbonate itself. Avoiding damage to this coating is also the reason why care should be taken when removing snow and ice from headlamps.

Cleaning agents that bring headlamps into contact with foam can have negative effects on their optical properties. If foam residue is still sticking to the lens at the end of the cleaning cycle, this creates problems with the light distribution – leading to glare or brightness reduction, depending on the lens area affected.

Good antifreeze products will specify their suitability for polycarbonate lenses on the packaging, and most reputable brands fulfill the necessary criteria. The suitability of a product for fan spray nozzles also indicates it’s a high-quality additive that does more than just facilitate cleaning and prevent water from freezing: the elegant telescopic nozzles in some cars require the water to have a slightly viscous quality in order to function correctly. Hard water, however, can have a negative effect on these nozzles and prevent them from extending. For people living in areas with really high concentrations of calcium in their tap water, it’s probably advisable to use distilled water instead. Although this obviously costs more than using simple tap water, it’s definitely cheaper than having to replace calcified nozzles. Because there’s a danger of calcification in other parts of windshield and headlamp washer systems as well, particularly in check valves, buying ready-mixed antifreeze is a good alternative. Diluting the concentrate with rainwater is a further – and particularly economical – option.

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