Chassis Cleaning

[Cleggy]

I wash under my bonnet twice a year and regularly do underneath with my machine, the MOT tester always says your cars are really clean and show no signs of corrosion.

Metal does not have to be dirty to corrode. My impression is that cars in Scotland corrode a lot because the winters are more severe than further south and more salt is used. Cars resident in coastal areas are also prone to more corrosion. The chloride ion has a fantastic ability to adhere to metal surfaces and initiate corrosion. Once on, it is very difficult to remove chloride using water alone; the Canadian Government has spent a lot of money researching this topic (their public service vehicles rot rather quickly) and the results can be found in the technical literature and are not merely "anecdotal". Cars more than ~5 years old and made of steel being corrosion-free is quite unusual.

Of course, MoT tests start at three years old and at that age they may well be corrosion-free, but it does start eventually and no amount of washing (alone) will stop that. My own two cars (average age 21 years) both have some corrosion on them, though not enough to ever get mentioned in MoT's. I attribute their good condition to the application of modern, corrosion-resistant paints and the rarity of salt on southern roads.