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Washing your car in winter

Short answer: wash every one to two weeks while the roads are salted, always with an underbody rinse, and on a day that is a few degrees warmer than the ones around it.

Why salt is the real problem

Canadian road crews spread rock salt and spray brine — salt water, sometimes with calcium or magnesium chloride — to keep roads open. The mix clings to the underside of your car, stays damp and speeds up corrosion on everything made of steel: brake and fuel lines, the exhaust, the subframe, rocker panels and the lower edges of the doors. Dirt on the paint is cosmetic; salt on the underside is structural.

How often to wash

• Every one to two weeks while roads are white with salt.
• After every major storm, once the roads have dried and the salt is on your car rather than on the road.
• One thorough wash in spring, including the underside and wheel wells, when the salt season is over.

Which kind of wash in winter

An automatic or tunnel wash keeps you in a warm car and dries it before you drive off — the easy option on cold days. Pick the program with the undercarriage spray; it is often only in the mid-priced or top packages — more in our guide to the underbody car wash. At a self-serve bay you can aim the wand yourself: wheel wells, behind the bumpers, along the sills. Many bays are heated in winter, and the wand gives you control that no automatic has.

When it is too cold

There is no fixed limit, but below about −10 °C water freezes on contact with cold metal. Locks, door seals, wipers and the fuel door can freeze shut. If you wash when it is very cold:

• Choose a wash with a dryer, or dry the car yourself.
• Wipe the door seals and open and close every door once.
• Drive a few minutes and brake gently to dry the brakes.
• Better still: wait for a milder day — they come often enough between cold snaps.

What to rinse

1. Underbody — brake lines, subframe, exhaust.
2. Wheel wells — slush packs in there and keeps salt wet for days.
3. Rocker panels and door sills — open the doors; salt collects on the inner sills too.
4. Behind the bumpers and the licence plate.

Rust protection sprays and oil undercoating, common in Canada, help — but they work best on a clean underside.

Inside the car, salt ends up in the carpet — our guide to car wash vacuums covers getting it out. If you wash every week through the winter, a monthly membership may cost less than single washes.

Find a car wash near you or read how to get the most out of a self-serve bay.