I live in Quebec city in canada, lots of salt on our roads. I am personally against rustproofing with petrolium based products. They seem to attack the rubber bushings on strut mounts and swaybars etc. Is rustproofing cost efficient in the long run? Why not just wash the car more often?

You’re confusing rust-proofing with under-coating. Rust-proofing involves drilling holes in areas of the vehicle body so a substance can be applied to the backsides of body panels such as doors and quarter panels. Under-coating involves appling a thick layer of a substance to the underside of the vehicle. This done to reduce road noise. If under-coating isn’t applied correctly, it can trap moisture and promote rust.


The factory rustproofing these days is pretty darn good, partly because of some chemical improvements they’ve made, but mostly because automakers have a better idea of why cars rust and design them to avoid traps where salty road grime will accumulate and to allow it to drain out easily. Aftermarket rustproofing is not only unnecessary these days, but it can actually cause the factory rustproofing to become less effective because it can clog some of the drainage channels or create new places for grime to accumulate.

Tester, I believe our Canadian friend is referring to the oil-spray “rustproofing” that is used up north, that’s re-applied every year or so.

I have to agree with Greasy. Your best bet is not to try and improve on a good system, you could make matters worse.

Agree; wash often, and try not to park the car in a heated underground garage.

I wholeheartedly agree with Greasy. Modern cars are designed with alloys, coating, physical configurations (avoiding cavities and providing drainage and ventilation where they’re unavoidable), bonding techniques, and even nonmetallic parts (polymers) specifically to prevent and avoid promoting rust. Aftermarket rustproofing applications can breech sealed areas, breech coatings, and clog vent holes. Rather than prevent rust, it can actually provide opportunities for it.

I strongly recommend against any aftermarket rustproofing on new cars.

Rubberized undercoating is different. That can be used if judiciously appled to reduce noise. It requires no holes to be drilled, however the person applying it needs to know what he’s doing such that he does not clog and drains or orafices. It should not be considered a rustproofing.

The old oil spray from many years ago is, simply, long since obsolete. It does nothing but make a mess.

I know what rust-proofing is. Years ago we used to drill holes in door’s and door jambs so we could spray oil into the box sections of the body so rust wouldn’t start from the backsides of those areas. I’ve lived in the snow belt all my life, and I know what rust-proofing is, and what under-coating is.


Yeah, I figured you knew what it was, I was just pointing out that the OP was not talking about undercoating; in fact, he never mentioned it. There is a proliferation of oil-spray “rustproofers” in the Quebec city area, it’s apparently still quite popular there. I assumed THAT process is what he was asking about.

What a lot of people are using now is the Spray on Bed-Liner stuff. Durable…and prevents rust. But MOST cars in MOST places don’t need it.