How do I check a used car for rust?
Where to Look
Rust often starts in areas that trap moisture and road salt. Check wheel arches, rocker panels, the bottom of doors, trunk seams, and the frame or subframe. Under the hood, look at strut towers and radiator supports. Also inspect the undercarriage and exhaust system.
Bring a flashlight and a small magnet. A magnet won't stick to plastic filler or fiberglass, which can hide rust repairs. Tap lightly with a screwdriver handle—if it sounds crunchy or flakes fall, rust is present.
- Wheel wells and fender lips
- Rocker panels and door bottoms
- Trunk floor and spare tire well
- Frame rails and subframe
- Exhaust and brake lines
Surface Rust vs. Structural Rust
Surface rust is cosmetic and can be sanded and painted. Structural rust—flaking, holes, or weak metal—compromises safety and is expensive to fix. If you see bubbles under paint or rust through a panel, walk away unless you're prepared for major repairs.
For serious inspections, pay a mechanic to put the car on a lift. They can check the frame and floor pans thoroughly. In rust-belt states, expect some rust on older cars; in dry climates, rust is less common but still possible.
Common mistakes
- Only looking at the body and ignoring the undercarriage, where rust is often worse.
- Assuming a fresh paint job means no rust—it could be hiding body filler over rust.
- Thinking surface rust is always harmless; if it's on a structural part, it can weaken the car.
