How to avoid buying a problem car with hidden corrosion.
Updated: Jun 1, 2019
As car enthusiasts, we've all been there… we see a car we dreamt about during our younger years, advertised cheaply in a classified ad and get excited.
Before we know it, we've made the call and arranged to see it!
But how can you safeguard yourself from buying a car that at first looks to be good, only to find out later - it wasn't the bargain you had thought, but an expensive money-pit project?
To an experienced eye, old cars each tell a story, and heavy corrosion on the underside is of vital importance to avoid.
Rust is caused by a mixture of electrolytic substances being flung up by wet tyres into the air, where they deposit themselves on the underside and other hidden parts of a car.
Sand, grit, salt mud and general grime coats the underside of cars in Europe (especially in wetter & colder countries) and slowly eat away at metal surfaces.
The first place to look for signs of corrosion is at the front of the car: This is where air (mixed with crap flung up by other cars during adverse weather conditions) is introduced to radiators and everything else behind it in the engine bay.
Factory new bolts and fitting in the engine bay are nickel plated, but with corrosion, they lose their coating and become rusty, eventually seizing themselves in place. Aluminium corrodes too, with a white furry layer forming on its surface. Intercooler and radiator fins can decay, so look carefully! If it's terrible at the front of the car, then you can be confident it'll be bad elsewhere too.
Look underneath at the subframe (this is an excellent opportunity to check for oil leaks, damage from accidents, etc. too) for rust. Check the exhaust heat shields and exhaust system also. These can rust very fast in harsh climates.
Beware - Some owners cover the underside of cars with underseal, or even have the chassis components repainted in the same colour as factory, so it looks original and rust free to the untrained eye... until someday the coating comes off to reveal what's underneath.
Overspray or the wrong colours will give that game away to a trained eye. Use a Torch and take something to lie down on. Don't be afraid to prod with something sharp and solid, to check for heavy rust. Surface rust is OK, but where you see bad rust, there's a lot more that you won't see. Don't fool yourself into the belief this potential dream car's an exception. If it's got heavy rust in places, it will have several more problems than those you may see at first glance.
Usual places for heavy corrosion are where ever the wheels will have kicked up crud: Sills, chassis and suspension components, rear underside, exhaust and suspension components, etc.
Check inside wheel arches, fender recesses, behind bumpers & inspect bumper support beams. Behind plastic mouldings such as side skirts, dirt and moisture can be trapped too. Check there. It's not uncommon to find very bad corrosion behind such panels.
By this stage, you should already know if a car is worth continuing to inspect. We can usually tell within a few minutes and soon walk away when a car doesn't pass scrutiny, but then from decades of experience, we know exactly where to look.
If it's got no underseal hiding corrosion and the engine bay hasn't got lots of cancer, look at each panel next.
Start on the roof and gently pry away mouldings around the front and rear glass if possible. On some cars, trapped dirt and moisture will cause corrosion around the perimeter.
Work your way around. Tap panels gently. If there are flat areas that don't sound hollow, look for signs of body filler. A magnet can help confirm, where you're unsure there's filler. Just be careful of scratching the paint.
Bottoms of doors, boot lid, fuel filler lid, spare tyre well, behind headlights, under battery tray and other places likely to trap dirt & moisture, should all be checked.
Remember; if you see bubbling of rust on paint, the corrosion beneath will be at least 3-times larger than it would appear at first glance (& often much worse)!
We see some modern classics advertised as "restored", with previous rust having been treated, etc. & a lot of heavy bodywork completed. Where structural parts have had welding, or rust ground away, cut & replaced, or even panels replaced to address corrosion, beware. In our experience, such cars are rarely worth considering unless they've had VERY expensive restoration work done by very experienced professionals.
In our experience, rust ALWAYS comes back once it's set in, or will appear somewhere else later on original parts of a car that aren't replaced during restorative. It's just a matter of time.
As the old adage goes, "You can't make a purse out of a sow's ear".
If the car you thought at first was great turns out to display the warning signs, listen to reason in your head and walk away. You'll be happier in the end, to get a better car without corrosion and you'll enjoy it more!