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I just bought a new Toyota RAV4, and the salesperson tried to sell me rust-proofing (rust protection for the car). I thought that a new car already has this, so do I really need to do it again? - Flora in Mississauga, Ont.

Ever wonder why you don't see as many rust buckets on our roads these days? The difference between vehicles from the 1980s and modern cars is that galvanized metal is now used to prevent rust from occurring. Galvanization is the process of coating the metal with zinc to prevent corrosion.

So why are dealers even offering additional rust protection? Isn't galvanization enough?

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"One thing about coated metal is that it's a bit vulnerable to stone chipping. Most people, especially in Canadian winters, are driving in situations with stones and sand, and these can damage the paint and metallic coating, and leave the ferrous materials exposed to corrosion. Most vulnerable is the area inside the wheel wells, and immediately behind the wheels," says Dr. Joseph McDermid, a professor of mechanical engineering at McMaster University.

The RAV4 is made at Toyota's plant in Woodstock, Ont., and, according to Toyota Canada, is manufactured with materials and coatings that help inhibit the formation of rust. Toyota offers a 60-month, unlimited kilometre corrosion perforation warranty on new vehicles. That means your new RAV4 is guaranteed not to rust through for at least five years, no matter how much you drive.

Toyota offers additional information in the Owner's Manual Supplement to help protect your vehicle against corrosion. These tips include immediately touching up any stone chips or scratches in the paint; repairing your vehicle as soon as possible if it's damaged due to an accident, or any other cause which destroys the paint and protective coating; and hosing off the undercarriage at least once a month, especially if you've driven on salted or dust controlled roads, or near the ocean.

On top of the manufacturer's built-in corrosion protection system, some dealerships offer additional rust protection packages. These can range in price from a few hundred to well over $1,000. They vary from a protective coating sprayed on the underbody of the vehicle, to full-body and interior packages with electronic corrosion protection.

An electronic corrosion protection system is a block of metal placed under your car with an electrical connection, which will corrode instead of the metals in your car. It's a standard corrosion protection technique, called cathodic protection, which is used in gas and water pipelines.

"Cathodic protection has a very firm fundamental electrochemical basis. It's pretty smart; but you've already got that in your car. The metallic coatings are a form of cathodic protection. The metallic coating - the zinc - will corrode before the steel does. So all you're doing is putting another chunk of metal onto a system where there's already a bunch of metal to do the same job," says McDermid, who also holds a Natural Sciences and Engineering Research Council of Canada/U.S. Steel Canada/Xstrata Zinc Industrial Research Chair in Zinc-Coated Advanced Steels.

"My opinion is that offering additional rust-proofing is a bit of a scare thing. But what I would always personally do is make sure you have your wheel wells sprayed, because those rubbery, rust-proofing coatings help protect the wheel wells from stone-chipping damage. I also think mud flaps are a really good investment, because they help prevent stone chipping," says McDermid.

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Many car manufacturers already have rubberized coating inside the wheel wells, so check this before you take action. If you're going to opt for a spray-on undercoating, it's imperative that the area is spotlessly clean.

Other motorists swear by oiling the underside of their vehicles. Oiling is temporary though; it's like applying furniture polish. You have to do it repeatedly, as with any regular maintenance. Again, the vehicle should be clean. Some mechanics and motoring enthusiasts argue, however, that an oily underside traps dirt and moisture, and can lead to corrosion.

Note that Toyota is not able to endorse any additional form of rust protection offered by dealers, nor is Toyota responsible for any problems that may arise as a result of their use.

With a brand-new car, you can enjoy the peace of mind that comes with an anti-perforation guarantee, and the corrosion protection system already designed into your vehicle. Make sure you keep your car clean, and if you're really worried, treat your wheel well area to a good protection coating.

E-Mail Ask Joanne at globedrive@globeandmail.com

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