Where should WD40 not be sprayed on a car?

From a mechanic’s perspective, WD-40 is a quick fix but not a long-term solution. Avoid using it on rubber seals, such as those around doors or windows, as it can cause them to swell or degrade. Similarly, steering and suspension bushings rely on specific lubricants—WD-40’s solvent properties can break them down faster. Stick to silicone-based sprays for rubber components.

WD40 is known as a moisture-displacing, anti-rust lubricant ("Water Displacement perfected on the 40th formula"). The 'W' in WD40 stands for water, 'D' for displacement, and '40' represents the 40th attempt. The name WD-40 was taken directly from the research notes of the chemists who developed it in 1953.

WD40 is a powerful rust remover with a wide range of uses, but it is not a universal solution and can have adverse effects on certain materials. Therefore, it should not be sprayed on rubber, plastic, or wax. Examples include tires and the car's exterior.

Natural rubber can swell after prolonged exposure to WD40. WD40 can also soften wax cleaners and some wax coatings. When thin, transparent polycarbonate or polystyrene plastics come into contact with WD40, they may crack or develop stress fractures.