Symptoms
- Visible orange-brown corrosion in wheel arches or under the car
- Flaking, bubbling, or scaly metal surfaces
- Possible rust dust or flakes visible after driving on rough roads
- Advanced cases may show holes or crumbling metal
Likely causes
- CommonRoad salt and winter driving conditionsSalt is highly corrosive and collects in wheel wells and the underbody through winter.
- CommonDamaged or missing splash guards/linersThese plastic liners protect the wheel well metal; when missing or cracked, rust accelerates.
- PossibleAge and general wear of undercoatingFactory rust protection wears thin over many years, especially with regular road exposure.
- PossibleTrapped mud and debris holding moisture against metalPacked mud in wheel wells keeps metal wet longer than it would otherwise be.
What to do
- Wash the undercarriage and wheel wells regularly, especially after winter driving on salted roads.
- Remove built-up mud and debris from wheel wells, which traps moisture against the metal.
- Inspect wheel well liners for damage and replace or repair them if missing, since they offer real protection.
- Treat light surface rust with a wire brush, rust converter, and appropriate coating or undercoating product.
- Have a body shop assess any area where metal feels soft, crumbly, or has visible holes, since this can be more than cosmetic.
- Consider an annual undercoating or rust-proofing treatment if you live somewhere with heavy winter road salt use.
Tools and parts
- Wire brush
- Rust converter
- Undercoating spray
Rust converterSearch: “automotive rust converter”
Wheel well linerSearch: “wheel well liner for [year make model]”
Undercoating spraySearch: “automotive undercoating spray”
When to call a pro
See a body shop if rust has caused visible holes or the metal feels structurally weak, since that goes beyond a surface treatment.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.