How often should you wash your car in a Chicago-area winter?

Why salt matters more than the dirt you can see

Road salt and brine are corrosive to bare metal. They collect in seams, on brake and fuel lines, inside the rocker panels and under the bumpers, and they keep working as long as they stay damp. A car that looks only a little grey on the doors can be carrying a lot of salt underneath.

Corrosion speeds up with moisture and with temperatures above freezing, which is why a January thaw is the moment that matters most. When the slush turns to puddles, go and wash.

What to buy

The underbody rinse is the part of the wash that earns its money in winter. Pick a package that includes it, or a wash that includes it in every package. A spray wax or ceramic top-coat is optional; it helps the next layer of slush slide off, but the rinse underneath matters more.

At the pace of a wash every week or two, an unlimited membership almost always costs less than paying per wash. Each review on this site gives the break-even number.

Avoiding frozen doors and locks

Wash in the warmest part of the day. On a bitterly cold morning, water in the door seals, the mirror housings and the fuel door can freeze before you get home.

Choose a wash with strong dryers, and before you drive away open each door and wipe the jambs and the rubber seals with a towel. That thirty seconds is the difference between a clean car and a car you cannot get into the next morning.

Dryer quality is part of the Dry & Finish score on every review here, for exactly this reason.

Short answers