How Road Salt Causes Cars to Rust: Prevention & Regular Maintenance Tips

March 14th, 2016 by

Road SaltWinter driving in Southwestern Pennsylvania can be interesting to say the least. We have to deal with our fair share of snow, freezing rain, and of course, rust. A necessary evil of sorts, road salt does a great job of melting down icy surfaces. On the other hand, it can wreak havoc on our vehicles, especially the undercarriage, wheel wells, brake lines, and other exposed metal.

Given sufficient time, any iron mass will eventually convert entirely to rust and disintegrate. Modern cars are primarily made from steel, which is an alloy of iron. Even automotive steel designed for rust-resistance will eventually give way to rust as seen in areas with heavily-salted roads. Aluminum-bodied cars and trucks, like the new Ford F-150, are very popular as their lightweight bodies are better on fuel economy and aluminum does not rust.


Exposing your car to water and oxygen is all that is needed to initiate the process, which is why new cars come with protective coats of paint and other sealants. Municipalities in areas of heavy snowfall will typically spread a mixture of salt and sand over the roads to make them safer for travel. Sand provides additional traction, while salt melts the snow and ice and prevents it from freezing over. Road salt keeps the roads safe for driving, but it’s like throwing gasoline on a fire when it comes to rusting out a car, acting as a catalyst by accelerating the corrosion chemical reaction process.

Rust is a result of an electrochemical reaction, in which iron meets oxygen to form iron oxide. Unprotected iron will corrode even in the driest of climates because it openly gives its electrons to oxygen. When the iron is exposed to water or even moisture in the air, the process is sped up dramatically by bringing more oxygen and carbon dioxide in direct contact with the metal and by acting as an agent for electrolysis. All this rust cocktail needs now is a few free-floating ions.

The free-floating ions of sodium and chloride in road salt work to reduce the freezing point of water, but the impurities within the salt mixture are then flung up into your vehicle’s wheel wells and undercarriage. Over time, continual exposure to water and road salt will break through your cars protective layer and rust will form.

Road Salt


Rust prevention should begin before the first snowfall. A little car maintenance might be all you need to keep your vehicle rust-free for years. Before winter hits, it’s recommended to apply a coat of wax and a wax sealant to your vehicle and its underside. This should be done only after the car is throughout washed and dried.

While under the car, pay close attention to common areas for rust and corrosion, including brake and fuel lines. Throughout the winter season, regular car washes should be performed, making sure to get into the wheel wells and undercarriage. You may also elect to have your car re-waxed and sealed when it is washed to increase its protection. Make sure it’s dried thoroughly and that you do not wash your car in below freezing temperatures as this can result in doors being frozen shut and other issues.

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