Rust had always been a problem for aging automobiles, particularly for those built in the 1960’s and 1970’s. As automakers tried to reduce the weight of automobiles, the problem seemed to get worse, due to the thinner steel being used. Today, improved body metals that resist rust, along with rust-discouraging vehicle designs and better primers, have helped to virtually eliminate rust altogether. Improved corrosion-fighting in cooling and exhaust systems have helped as well.

The improvements add roughly $200 to the cost of new cars, but this cost is worth it. According to the National Highway Traffic Safety Administration, in 1977 half of all U.S. passenger cars lasted 10.5 ears, with a travel lifetime of 107,000 miles. By 2001, which is the latest year studied, the median lifetime for passenger cars reached 13 years, with a travel lifetime of 152,000 miles. Better rust resistance slows depreciation and helps to keep resale values up.

In order to combat the rust problems, automakers started to coat their steel with metals such as aluminum and zinc or their alloys. Although these metals oxidize, the resulting corrosion products are white and less noticeable. When aluminum and zinc are present, they oxidize while the steel does not. Automakers found that metals coated with zinc were hard to paint, and the paint tended to flake off. This problem was solved by dunking the car’s body in a phosphate bath, creating a thin, paintable layer of phosphate crystals on the metal surface. Ensuring that primers and anti-rust waxes got into the hard-to-reach crevices and inner surfaces like rocker panels, is important as well. Automakers also found that vehicle design had been contributing to rust problems as well, and have worked to eliminate joints and pockets in which “muddy, wet wads of leaves and debris soaked with road salt” would collect.

Source: Frank Greve, “Cars last longer with rust on the run."