Rustproofing Your Car

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By Shari Prymak

Rust is an electrochemical reaction which occurs when water contacts bare steel. Creases or depressions in the metal can trap moisture, increasing contact time which causes more rusting to occur. The rate of rusting increases with temperature.

Vehicle rusting began to be a serious problem in the 1950s when increasing amounts of salt (mostly sodium chloride and sometimes calcium chloride) started being used as a safety measure to melt road ice in winter. Saltwater spray trapped in metal vehicle folds and creases doesn’t freeze and the salt content greatly accelerates the rate of corrosion. Calcium chloride can also draw moisture from the air, so the salt accumulated in the winter can continue to cause rusting in summer, even when there is no water on the roads.

Unlike such places as Arizona and Alberta where salt is never or seldom used and the dry air or extreme temperature naturally inhibits corrosion, Ontario’s moderate climate puts it in what is often called the Rust Belt.

Rustproofing vehicles began as a major business in the 1960s and 1970s when body panels and floors started rusting through after only a few years, largely due to the increased use of road salt. Since then, manufacturers have learned how to better coat the metal used to make their vehicles, replace steel with materials that don’t rust, and avoid water accumulation by eliminating vulnerable creases and depressions and adding numerous drain holes. As a result, vehicles are now lasting longer, even without additional rustproofing.

However, because vehicles are on the road longer, other parts, such as brake and fuel lines, cooling and power steering tubes, and electrical connectors have become more likely to rust and corrode during the life of the vehicle. These parts can cost several hundreds of dollars to replace and many knowledgeable mechanics feel that a careful rustproofing every year or two with a light oil-type treatment can greatly prolong the life of these components and significantly reduce maintenance costs. Such treatments cost about $100 – $140 for a typical car.

Rust treatments using thick coatings (once called “undercoating”) are also available and are an additional source of revenue for many vehicle dealers. Such treatments can be expensive and are generally not recommended (except by those who sell it). Not only do thick coatings not protect many of the parts a fine oil-based spray reaches, but if improperly applied may actually promote rust by plugging critical drain holes.

Because corrosion is an electrochemical reaction, electricity can, in some cases, be used to stop or slow the reaction. So-called “cathodic” corrosion protection uses a negative electrical charge applied to the protected metal. Cathodic corrosion protection has been around since it was first used for ships in 1824 and continues to be a proven way to protect metal in such applications as pipelines and storage tanks.

Auto dealers have recently begun to heavily promote electronic rust inhibiting systems costing several hundreds of dollars. However, just because applying an electrical charge reduces corrosion under certain specific conditions, or in laboratory tests using simple pieces of sheet metal, does not mean it will provide any significant protection for a motor vehicle in everyday use. The difficulty with determining the effectiveness of an expensive cathodic rust inhibiting device, is that a consumer will only know if it doesn’t work years after he or she has paid for it. If ever. Even if electronic rust inhibiting devices could protect all the sheet metal of a vehicle, it has not, to our knowledge, been shown to protect the more vulnerable lines, pipes, and connectors.

In the end, go with the tried and true oil-based method if you want additional corrosion protection for their vehicle.