What winter does to a car
In cold regions, road crews spread salt, brine or other de-icing materials to keep roads from freezing. These work well, but they are rough on cars. Salt dissolved in water forms a conductive solution that speeds up rusting, particularly where bare metal is exposed. Mud and sand hold moisture against the car and also grind into paint as it dries. Together they can shorten the life of bodywork, brake parts, exhaust parts and other components.
The details vary. Treatments used on roads differ between regions, and some are more aggressive than others. Cars in areas with no winter road treatment face a lighter version of the problem, though coastal air can contain salt too.
Where the damage starts
Most corrosion begins where moisture and salt stay trapped:
- the underside of the car, including the floor pan, frame and suspension parts
- wheel wells and the inside of fenders, which catch spray
- door sills and the bottom edges of doors and the trunk lid
- areas around chips and scratches in the paint
- brake lines, fuel lines, exhaust parts and fasteners
- the lower edges of the windshield and around trim
Paint and underbody coatings protect the metal. Once a stone chip or scratch exposes bare steel, rust can start there and spread under the surrounding paint. Catching this early is much easier than repairing it later.
When to wash
During winter, rinsing off salt regularly matters more than a perfect finish. As a rough guide, many owners aim to wash every couple of weeks in salty conditions, and after any particularly heavy salting. The actual frequency depends on your climate and how often roads are treated.
If temperatures are below freezing, wash on a day when it is above freezing if possible, or use a facility where the car can be dried inside. Water can freeze in door seals, locks and brake components. Afterward, wipe the door seals and drive gently for a few minutes, applying the brakes lightly to help dry them.
A thorough clean in early spring, once the salting season is over, is the most important wash of all. The benefits of regular washing include exactly this: removing corrosive material before it can do harm.
How to wash off salt and mud
You can use a commercial wash or do it at home.
At a car wash. Choose one that offers an underbody rinse, which uses sprayers to reach the underside. Touchless washes avoid contact with the paint, while brush washes vary in how well they are maintained. Choose whichever you are comfortable with.
At home or at a self-service bay:
- Rinse the whole car first with plenty of water to loosen mud and sand before touching the paint. Wiping dry grit around is what scratches it.
- Spray the wheel wells, underside, door sills and lower panels thoroughly, angling the hose to reach behind the wheels.
- Wash from top to bottom with a car shampoo and a clean wash mitt, rinsing the mitt often.
- Clean wheels and tires last with separate tools, as they carry the most grime.
- Open the doors, hood and trunk and wipe the jambs and seals, where salty water collects.
- Rinse well and dry with a clean microfiber towel or chamois.
Avoid pressure washers held very close to the paint, trim or electrical parts. Take care with the engine bay, which should only be rinsed gently, if at all, with sensitive parts covered.
Check for damage as you go
Washing is a good time to inspect. Look for:
- stone chips and scratches that reach bare metal
- bubbling paint, which can mean rust forming underneath
- rust on exhaust parts, brake components and suspension arms
- damage to underbody coating or mud flaps
- heavy deposits inside the wheel arches
Small chips can be touched up with paint made for your car’s color code, and some owners treat minor surface rust with a rust converter or primer, following the product directions. Anything deeper, structural or near brake and fuel lines deserves professional attention, since corrosion can affect safety. An inspection can also catch it, as a safety inspection may check for rust in key areas depending on local rules.
Protecting the car for next winter
- Wax or sealant. A layer of protection helps water and dirt to run off and makes washing easier. The benefits of car waxing include a barrier that slows paint wear, though it does not replace rinsing.
- Underbody coatings. Some owners have rust-proofing applied by a professional, especially on a new car or a car kept for many years. Quality and value vary, and manufacturers’ warranty terms can be affected, so ask questions and read the conditions first.
- Fix chips promptly. Sealing small chips stops moisture getting in.
- Keep drains clear. Door and sill drain holes can clog with leaves and mud, trapping water.
- Store carefully. A car left parked for a long time with salt on it can develop problems, so wash it first. Notes on vehicle storage cover this further.
Interior salt
Salt and slush also come inside on shoes. Use rubber mats in winter, and shake or vacuum them out regularly. White salt stains on carpet can be dissolved with a mix of warm water and white vinegar, tested first on a hidden area. Drying the interior helps prevent musty smells and window fogging.
Keep it in proportion
A little surface dirt is harmless. The goal is to stop salt and wet mud from sitting on the metal for weeks or months. A regular rinse in winter and a thorough clean in spring will go a long way towards keeping rust at bay.