AI DamageShort answer
The rust belt is the group of northern and north-eastern US states where roads are salted in winter. Over the years salt eats the underbody, brake lines and fasteners. The body can look fresh on top while the subframe underneath is rotten.
Where roads are salted
The main regions are the Midwest and the Northeast: Michigan, Ohio, Illinois, Wisconsin, Minnesota, Pennsylvania, New York, New Jersey and the New England states. Cars from Canada carry a similar risk. The coast is a separate case: sea air in Florida or along the Gulf of Mexico also speeds up corrosion, especially after storms.
The South and Southwest (Arizona, Nevada, Southern California, inland Texas) are the driest regions. Cars from there usually have the best underbodies.
The auction location is not where the car lived
A lot is sold where the insurance claim happened, not where the car spent its years. A Michigan car can end up in a Georgia yard after its owner moved. So check the VIN history: which states the car was registered in and for how long (see VIN decoding).
Where to look for rust in lot photos
| Where to look | Sign |
|---|---|
| Sills and lower door edges | Bubbling paint, rust streaks, holes |
| Wheel arches | Brown deposits on the arch lip, peeling protection |
| Bolts and nuts in the engine bay | Rust-coloured fasteners that are silver or black on a fresh car |
| Brake discs, callipers, control arms | Deep rust and flaking metal rather than light surface bloom |
| Exhaust system, if visible | Holes and patches on the silencer |
Light surface rust on discs after a few weeks at the yard is normal. Rust on fasteners and body edges is the warning sign.
Why rust makes a crash repair more expensive
- Seized bolts snap during teardown. Instead of removing a part, the shop has to drill out the fastener.
- A new part will not mount on a rotten base. The shop repairs or cuts out more than the estimate assumed.
- Body geometry is harder to restore when mounting points are weakened by corrosion (see body geometry).
- Brake lines and fuel lines in salt states often have to be replaced along with the repair.
What to do before bidding
- Check which states the car lived in, not just where the lot sits.
- Zoom into photos of the underbody, arches and engine bay. If there are none, treat the underbody as unknown.
- For an older car from a northern state, budget a reserve for fasteners and lines.
- After purchase, inspect the car on a lift before the repair starts, not after.
Related: suspension and wheels after an impact.