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Can you wash your car too much?


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Scotty, there are those online saying that you shouldn’t wash your car at a retail location during the winter because the water is likely contaminated with salt, mag-chloride, etc. from previous drivers and if the wash doesn’t properly filter the water you putting activated salt in water solution onto your car which can accelerate rust.  Is this correct or just something interesting to talk about online? I have also read online what sounds like paranoia.  People are saying you can wash your car too much and cause rust/corrosion to the parts underneath your car.  Is this accurate, can you wash your car too much?

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Rust forms as a result of non-pure water and oxygen coming in contact with steel. Pure water (deionized water in a lab, or distilled water at home) doesn’t rust steel very quickly because 100% water isn't electrically conductive. It's the dissolved stuff in water that allows it to conduct electricity and leads to rust. Dissolved salts are excellent conductors of electricity. It's complicated chemistry, but basically water gives oxygen in the air a medium to oxidize (rust) steel if it can conduct electricity. If you washed your car with distilled water, it would take a very long time to rust. No car wash uses pure water, so the theory is somewhat correct. Saltwater is far more corrosive than ordinary city water, so it will take a very long time. You can try it out, get 2 ordinary steel bolts from the hardware store, put one in a glass of distilled water or tap water, and put the other one in a glass of water with very high salt content and let them sit for a while. 


I have heard this about car washes as well. I'm not sure if it's true or not. Generally the more expensive car wash joints won't do this, they make you pay more for the wash so you get fresh water every time. Self-wash bays absolutely don't do this. 

@Justin Shepherd Thank you! I contacted the car wash and they explained how proud they are of their reverse osmosis water filtration system indicating that the water is reused about 3 times after passing through the reverse osmosis filter, then they freshen the water after every third or fourth wash. I have heard that RO filtering is very good, so I assume this is ok.


Reverse osmosis is an excellent, albeit expensive, way to purify water.

As long as you aren't washing your car with salt water, you'll be fine. I have an unlimited car wash package for my vehicles and my daily drivers get washed nearly every day, sometimes twice a day. Never have had an issue. I do use an upscale wash, not a gas station special though.

@Mod_Man Very good to know, thank you! I too am using a subscription service and not one tied to a gas station. It seems like a pretty good wash.

@mod_man, I hear you but if I washed my daily driver it would just loosen up the metal tape on all the rust holes. Silly

Laugh Well if I lived up North (I wish) I'd probably have a beater to drive since the roads are bad and the winters are salty. Here in Houston, the roads are bad but snow is a freak thing. So not too much to worry about.