In much of North America the last snow of the winter usually occurs sometime in February or March, which is also the time of the last road salting. Once the salt is gone — and it’s good to wait until there’s been a heavy rain that gives the roads a good rinsing — you will want to get the road salt off your car. You could go to the local car wash and spend money … or you could avoid convenience and save money by doing it yourself. I’ve always gotten good results with a bucket of warm water mixed with a little dish-washing detergent. Apply with a large sponge, scrub, dump the remaining detergent-water mix over the car, and rinse well.
However, removing the road salt from your car’s unpainted undercarriage is even more critical than washing the car’s body. It’s the metal parts under the car that can be damaged by salt’s corrosive powers. The painted body can usually withstand contact with road salt pretty well. Also, the top of the car gets rinsed by the rain. The underside of the car isn’t exposed to rain. Most people know this, which is why commercial car washes offer an “undercarriage wash” and why they do such a good business after the end of the snowy season.
But you don’t need to pay $$$ (not to mention, wait in a long line) to give your car’s undercarriage a good washing. You can just use a garden hose and a sprinkler. When I wash the car for the first time after the last of the winter snow, I attach a lawn sprinkler to the garden hose, turn on the water, and use the hose to slowly push the sprinkler back and forth under the car. It’s a good idea to avoid spraying too much water into the engine compartment. You might need to get down on your hands and knees to make sure the water is directed at the wheels and suspension. There are actually special tools that attach to a hose to perform the undercarriage washing. Some clever people have made their own. In my honest opinion, it seems that a lawn sprinkler works just as well. The whole point is to get the salt off your car, and because salt is water-soluble, all you really need to do is get water into contact with the underside of the car.
It takes a little time, but … as usual, avoiding convenience means you’re paying yourself instead of paying someone else.
(However, if you search the internet you can find lots of people saying that you need to use some kind of special salt-removing product to really do a good job. All I can say is that the sprinkler method has worked for me, but as the saying goes, your mileage may vary. What’s happened to me is anecdotal. I haven’t owned enough cars to do a scientific study. It might be that my car is less susceptible to rust or maybe I reduce my driving when roads are icy and salty. (The second part is true. I really do try to avoid driving when there’s ice and snow on the roads.)