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Rustproofing/under coating

I know that all cars are “rustproofed” from the factories. My daughter lives in New Hampshire, lost of salt on roads in winter time, lots of “salty air” all the time being so close to the ocean. She just pruchased a 2011 Honda Fit, and wants to be ultra sure that it doesn’t rust or have the aluminum parts deteriorate. Any thoughts about this? Thanks

Adding additional “rust-proofing” to the underside of a vehicle really won’t help, and in some cases, may cause more damage. That stuff can hold onto debris and actually cause more damage over time.

The best thing she can do is wash it. Frequently. In a car wash that cleans the underside of the vehicle. When I’m up North, I do mine once a week, minimum, unless I park it in a garage and don’t drive it.

Frequent washing and waxing is the answer.

Aftermarket rustproofing often causes problems, such as sealing up drain holes that are meant to be open.

Rust proofing was a booming after market business in the late 60’s and 70’s where salt was used on winter roads. However the rust proofed cars rusted out at about the same rate as the untreated cars. So, sales of the process dropped off. Then auto mfg’rs got tired of the complaints when new cars developed holes in the fenders at 3 years or less old.

Eventually new treated steels were used to deal with salted roads and today the cars are much more “rust protected” because it is built into the design of the car from the outset.

Therefore additional rustproofing isn’t needed. And, if poorly done rustproofing can be rust creating. Aluminum doesn’t rust, it does oxydize. Best you can do is keep it clean. Cars in the north look different underneath and the mechanics in Florida can tell a “northern car” for a local Florida car; then can see the rust on the suspension components. In effect, it is part of life driving in the Northern parts of the US.

Manufacturers today design rust resistance into the cars by the use of drainage and venting, non-metallic parts, automatied welding processes that have far less effects on base metals, electrostatically applied coatings on structural assemblies, the use of bonding processes instead of welding, more rust resistant alloys, and numerous other measures. Adding aftermarket rustproofing cannot add to that, only compromise it by providing a path where none should be or restricting a vent hole or drain path.

“Undercoating” is either rustproofing or “rubberized undercoating” which really only adds sound dampening…and not much at that.

In short, don’t have any of these processes done.

And, by the way, I live in NH too.

You can count this as one more vote for doing the following:

Keep the car–including the undercarriage–as clean as possible, especially in the winter.
Apply touch-up paint to chips and scratches as soon as you see them.
Wax the car a couple of times per year.

If this was the '50s, '60s, '70s, or even the '80s, I would advise you to have the car undercoated/rustproofed. However, technology has advanced considerably since then, and the car manufacturer’s rust prevention is actually very effective at this point.

Like MB I too live in NH.

We’ve kept 4 vehicles past the 250k miles mark…and at most one of them showed a little rust after 9 years. Now 20 years ago I’d say yes it’s a good idea (IF DONE CORRECTLY). But manufacturers have learned how to make cars NOT rust…

I would suggest that you DON’T keep the car in a heated garage during the winter months. Rust occurs above 32 degrees, and the combination of the salt and crud under the car with melting snow and water will speed up the rusting process. Washing the underbody is a good idea but most people don’t bother, Women especially. My Wife has never . . not once . . . washed her car, nor even taken it to a car wash. Rocketman

Chances are, she’ll be rid of the car before any real rust damage occurs