With the possible exception of people who lease cars, rust is every car enthusiast’s worst nightmare. Having invested time and money in an exotic car does not make rust any less nightmarish to say the least. Rust is inevitable. Nature eventually reclaims everything. However rust can be postponed for a long time with a little TLC.
The thing to remember about rust on a car is that serious rust starts on the inside. Don’t worry too much about paint chips. Chips don’t look good, but the surface rust that develops there often never amounts to much because it’s usually dry. The nasty stuff grows on the bottoms of your doors, in the rocker panels, wheel wells, under windshield gaskets, etc. By the time most owners see that kind of rust, serious, expensive damage has already been done. That kind of rust is like the proverbial iceberg; there is much more below the surface.
When washing your car, equal attention should be paid to the underside and the exterior. Make sure there are no piles of dust and road debris inside the wheel wells that can get wet and stay wet for weeks. Make sure that all splash aprons are in place but occasionally remove them to inspect and clean behind. Remove interior panels and clean out debris that tends to collect in door bottoms. Make sure all drain holes are free and that everything is dry, particularly the crevice formed by the outer door skin and the door frame coming together. It’s a good idea to blow this crevice (called a ‘pinchweld’) out with compressed air and squirt some penetrating oil down there and up the sides to displace any water deep inside. Follow that a few days later with an oil pump can filled with motor oil. Some people like to use wax-oil or similar products which are thicker than motor oil and stick to vertical surfaces. The problem with those products is that if they are not used properly they plug up drain holes and make the situation worse by trapping water and they just can’t penetrate into trouble spots like pinchwelds.
A hand pumped garden sprayer can be filled with oil and the spray wand poked inside areas otherwise inaccessible. You may have to drill some holes under sill plates and other hidden areas to gain access to rust-prone regions of your car. Don’t forget to clean and spray around the gas tank and in the bottoms of the rear fenders – any place where dirt and water can hide and wreak havoc.
Do the job on a large, heavy duty plastic sheet and let your car sit and finish dripping for a few days with the doors open. Most of the oil that falls to the floor can then be squeegeed and reclaimed.
A word about undercoating: this product is often mistaken for rust proofing material. Actually, it’s used more to deaden road noise and can actually promote rust when it dries and cracks to form water-trapping pockets. It’s a good practice to inspect every inch of the bottom and remove any cracked or loose undercoating with a heat gun and a scraper. A propane torch will work also. Make sure you have good ventilation and safety equipment such as a hat, goggles, gloves, and long sleeves.
Spraying oil on old undercoating that is not loose will help rejuvenate it, if you don’t want to redo all the undercoating. Don’t spray the exhaust system or rubber parts.
Check under the carpeting and see that it’s dry under there. Water leaking in from rain or car washing is not uncommon and wet carpets can cause serious floor rot.
If rust is starting to grow along the windshield or rear window gasket, the best cure is to cut the gasket with a razor knife and carefully take the windshield out. You can now sand, prime, and paint the offending area and have the windshield installed with a new gasket. Left alone, this kind of rust will eventually turn into a hole.