Where to find rust on your car
The nasty little rust bug, starts at the bottom of the car where moisture and water collects and then eats its way upwards through the bodywork. What you have to distinguish between is serious (structural) and superficial (minor) rust. Look underneath the car without jacking it up and using a torch. Inside pull up the carpets especially if they seem to be damp. The area adjacent to the doors is the most common area for rust. On the bodywork it should be really obvious because of bubbling and discolured paintwork.
How to find rust on your car (or one you're looking to buy)
If the rust is not obvious magnets will not stick to rusted or filled areas and replacement plastic body panels. If you suspect any area, be subtle and with a magnet (put it in your palm) and cover it with a layer of paper so that it does not damage the paintwork. Be aware that some cars may have some plastic or aluminium panels as standard.
Hands are very sensitive instruments indeed. Running the palm over the bodywork can pick up imperfections and filler very quickly. Press any suspect parts of a panel with your fingers and feel for any give, which suggests filler, or rust underneath, especially if you hear a 'cracking' sound.
What is minor rust?
The car may be full of holes but it can still be perfectly legal. Generally, minor rust on the edges of panels is rarely serious, so a rusty bonnet, doors and wings can easily be lived with, or simply repaired.
What is structural rust?
Structural rust is more serious can make the car unsafe and will result in an MOT failure as the important load bearing areas of the car can no longer take the strain. The problem is that whereas most mechanical parts can be easily and cheaply replaced; serious rot is too uneconomic to repair. If you think that the rust is serious then forget it.
How to remove rust
If it is worth you while and you don’t want to pay a professional to do the job, then first of all you need to remove the surface rust with a wire brush or sandpaper. Then find a product that you can apply to kill or neutralise the rust. Finally, you may need to paint the affected area.