Symptoms
- Live somewhere that uses road salt in winter
- Notice surface rust starting on the frame or wheel wells
- Car is a few years old and hasn't had an undercarriage wash
Likely causes
- CommonRoad salt buildup left on the undercarriageSalt accelerates rust significantly and clings to the underside long after roads are clear.
- CommonSurface rust left untreatedSmall rust spots can spread and eventually compromise metal if not addressed.
- PossibleScratched or chipped undercoating exposing bare metalRock chips and road debris can wear through protective coatings over time.
What to do
- After winter driving on salted roads, get an undercarriage wash (many car washes offer this as an add-on) every few weeks through the season.
- Inspect the wheel wells, frame rails, and exhaust for early surface rust using a flashlight.
- Treat small surface rust spots with a wire brush and a rust converter or rust-inhibiting paint before it spreads.
- Consider an annual undercoating or rust-proofing treatment if you live in a heavy salt-use region.
- Keep drain holes in doors and rocker panels clear of debris so water doesn't pool and rust from the inside out.
- Address any paint chips on the body promptly with touch-up paint to prevent rust starting points.
Tools and parts
- Wire brush
- Flashlight
Rust converter or rust-inhibiting spray paintSearch: “rust converter spray for car undercarriage”
When to call a pro
If rust has progressed to visible holes or affects structural areas like frame rails, have a body shop assess it, since this can affect safety and resale value.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.