Rust is one of the few car problems that only gets worse the longer you ignore it. A small chip in the paint can turn into a bubble, then a soft spot, then a hole, and once rust reaches structural parts like the frame, brake lines or suspension mounts it becomes a safety issue as well as a cosmetic one. Most of it is preventable with a little routine care, especially when roads are wet and salted.
How car rust starts
Rust is iron oxide. It forms when bare steel is exposed to water and oxygen, and it forms faster when salt is involved, because salty water conducts electricity and speeds up the chemical reaction. Modern cars use galvanized steel, primers and paint layers to keep moisture away from the metal, so rust usually begins wherever that protection has been broken or where water sits for a long time.
Common starting points include:
- Stone chips and scratches on the hood, the front edge of the roof and the lower doors, where the paint has been knocked down to bare metal.
- Wheel arches and rocker panels, which take a constant spray of water, grit and slush from the tires.
- Door bottoms and the trunk lip, where drain holes can clog with leaves and dirt and trap water inside the panel.
- The underbody, including brake and fuel lines, exhaust parts, the subframe and suspension components.
Why winter is the worst season for rust
Many northern states and cities treat roads with salt or salt brine to melt ice. It keeps traffic moving, but the slush it creates gets thrown into every seam and cavity under the car. Salt also keeps working after the snow is gone: if it isn’t washed off, it sits in crevices and keeps attracting moisture.
How to prevent car rust
Wash more often in winter, not less
It’s tempting to skip car washes when it’s cold, but winter is when washing matters most. Every week or two during salting season, rinse the car thoroughly, paying attention to the wheel wells, the lower panels and the underside. Many automatic car washes offer an underbody spray, which is worth choosing in winter. At home, pick a day when it’s above freezing so water doesn’t freeze in door seals and locks, and use a proper car shampoo rather than dish soap, which can strip wax.
Wax before the bad weather arrives
A coat of wax or paint sealant gives the paint a sacrificial layer that sheds water and makes it harder for salt and grime to stick. Late fall is the ideal time to apply it, while it’s still mild enough for the product to cure. A combined wash and wax product, such as the Car Wash and Wax Detailer Grade Soap, is a simple way to clean and top up protection in one step between full wax jobs.
Touch up chips straight away
Small chips are the doorway for most body rust. Clean the chip, let it dry, and dab on touch-up paint that matches your car’s paint code (usually printed on a sticker in the door jamb). It won’t look perfect up close, but sealing the bare metal is what counts.
Keep drain holes clear
Doors, rocker panels and the trunk have small drain holes along the bottom edge. When they clog, water sits inside the panel and rusts it from the inside out. Open each door and look along the bottom edge; a pipe cleaner or a thin piece of plastic can clear a blocked hole.
Look underneath a few times a year
You don’t need a lift to spot early trouble. On a dry day, with the car parked on level ground and the engine off, use a bright light to look behind the wheels and along the underside. A rechargeable LED work lamp makes this much easier than a phone flashlight. Look for flaking metal, orange streaks, bubbling undercoating and brake lines with heavy scale. If you need to raise the car for a closer look, use proper jack stands, never just the jack; our guide to car jacks and how to use them safely covers the basics.
Consider an undercoating or rust-proofing treatment
Shops offer underbody treatments ranging from oil- or wax-based sprays that creep into seams to harder rubberized coatings. Ask how often a treatment needs reapplying and how the shop prepares the surface, since a coating sprayed over existing rust can trap moisture.
How to deal with rust you already have
Surface rust
Light orange speckling on the surface, with no bubbling, is surface rust. You can usually fix it yourself: sand the spot to clean, bright metal, wipe it clean, apply a rust-converting or rust-inhibiting primer, then color-matched paint and clear coat. Our guide to automotive clear coat explains how the top layer protects the paint.
Bubbling paint
Bubbles under the paint mean rust has already spread beneath the surface. The visible bubble is usually smaller than the damage underneath. Small areas can sometimes be ground back and repaired at home, but the repair tends to come back if any rust is left. A body shop can cut out and treat the area properly.
Rust holes and structural rust
If you can push a screwdriver through the metal, or if rust is on the frame, subframe, suspension mounts or brake lines, have a professional inspect the car. These parts keep the car safe in a crash and keep the brakes working, so they aren’t a DIY patch job. Our guide to choosing the right auto body shop has tips for finding a good one.
A simple winter rust routine
- Before the first snow: wash thoroughly, wax, touch up chips and clear the drain holes.
- During salting season: rinse the car, including the underbody, every week or two, especially after a storm.
- Once a month: take a quick look in the wheel wells and under the car with a good light.
- In spring: give the car a deep clean underneath to remove leftover salt, then check for new chips or bubbles.
For more cold-weather preparation, see our guide to car accessories for winter, and for keeping the paint looking new all year, our introduction to automotive detailing.
FAQ
Does washing my car in winter cause rust?
No. Washing removes the salt that causes rust. Just let the car dry, wipe door seals, and avoid washing when it’s well below freezing so water doesn’t freeze in locks and seals.
Can I stop rust once it has started?
You can stop surface rust by removing it back to clean metal and sealing it. Deeper rust has to be cut out or treated by a professional, because any rust left under the paint keeps spreading.
Are newer cars still at risk of rust?
Newer cars are much better protected than older ones, but chips, scratches and clogged drains can still let rust in, especially in areas that use road salt.
We run the NicheStuff store; some links in this post go to products we sell.
Top image: Gabriel Jimenez, CC0 1.0, via Wikimedia Commons.