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Winter Weather Myths: Does Road Salt Actually Cause Rust on Cars?

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As snow falls from the sky and freezes on the ground, your neighborhood streets are no doubt covered in copious amounts of road salt, melting the ice and turning it into slush that leaves your car with a powdery white residue.

No doubt you’ve also seen people (those with money to spare) taking their cars through car washes to clean that residue off. At some point, you’ve been told by one of these people that road salt is “bad for your car” and that it’s important to rinse it off. But, how bad is road salt actually for your car? And if it is, what should you do about it?


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Understanding the Corrosive Nature of Road Salt

Even if you don’t live in an area where there’s snow in winter, your car will still eventually rust over time. This is due to the basic electrochemical reaction between iron and oxygen that forms iron oxide, which is accelerated by rainwater that contains traces of iron ions.

So why does everyone make such a big deal about how road salt is the perpetrator causing your car to rust?

The introduction of sodium chloride–the most common type of road salt–kicks this process into high gear. By reacting with the snow to melt it by lowering its freezing temperature, the material releases ions that accelerate the iron oxide process and even becomes acidic when reacting with hydrogen from the H20. Without getting too technical, all these ions mixing together causes a chain reaction that results in fast-spreading rust covering the undercarriage of your car.

To prevent this from happening, the DMV has a list of suggestions to follow:

  • Wax your car before the first snowfall to provide an extra layer of protection.
  • Treat the undercarriage with an anti-corrosion oil from a car parts store.
  • Wash the vehicle after it encounters lots of snow/salt, making sure it’s dried afterward
  • Avoid splashing into puddles or getting near salt trucks

Road salt does indeed play a dastardly part in the rusting of your car, so make sure you make the effort to keep it clean and dry!


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Sources: Hemmings, DMV