Relative values and mechanisms of Rust Check / Rust Coat / Rustproofing

I’m being forced by circumstance to get a car. For a variety of reasons, its looking like a new car may be the best option. When I talk to the dealer people, one of the options is rustproofing. Toyota offers a 12 year warrenty rustproofing for $399 Canadian, which seems pretty steep to me. Rustcheck charges $150, but you get it done every year. The Rustcheck dude suggested that Rustcheck does a more thorough job - rockers, door panels, etc., versus just the underbody from the dealer. My gut says any dealer accessory is overpriced, but I’d like to know if anyone has data on (1) the relative value of these two approaches, (2) the differences in mechanism and execution, if there are any, and (3) the general received view regarding rustproofing in general and dealer accessories in general.

Obviously if all I get are IMHO, then we’ll have to get shipped off there, but I was hoping for more authoritative answers first. Thanks in advance.

You don’t need anything, and the dealer undercoating could even be counterproductive.

Car makers and academia put some serious effort into the question of why cars rust in the 1970’s and 1980’s and what they discovered is that rusting was largely due to road grime accumulating places like behind the fenders and on the frame. They’ve since focused on improving drainage and eliminating places for grime to accumulate. This, along with improvements in metallurgy and paints, has made most cars sold in North America essentially rust proof right out of the factory (although we’ll see what happens with the new Fiats :)). Additional rustproofing these days is just a added dealer profit item and, like I mentioned above, some of the spray-on undercoatings can actually make things worse since they clog some of the drainage paths and allow crud to accumulate.

GreasyJack is 100% correct. add-on rustproofing is useless.

Yep, the entire body has rust-proofing electroplated on to it prior to being painted. Anything aftermarket is a waste of money.

OK, so why is there a rustproofing industry, and, no offense, but is there anywhere you could direct me to read more of these assertions?

because it might have been beneficial* up until the late '70s, when car bodies still had lots of crevices and pockets for salty muck to collect, and before pre-paint hot-dipping became common, but this is no longer the case. The existence of rust-proofing shops relies on people who don’t know any better.

look at any car on the road built in the last 10 years. I’d wager very few of them have had any aftermarket rustproofing treatment, and very few of them have much if any visible body rust. The ones that do, do so because of design shortsightedness (here I am thinking of Honda Accord quarter panels just behind the rear wheels, and the front lip of the hood on some Chrysler cars,) but these are areas where aftermarket rustproofing won’t treat anyway.

  • and frequently it still did more harm than good, as the practice at the time was to drill holes in the body in areas like the rocker panel boxes so they could spray in their crap, then put a plastic plug in its place. When I still wrenched it wasn’t uncommon to see a car with those Ziebart plugs in the door sill, with a nice big hole rusted through right next to it.

Gee, I thought I was going to be able to find oodles of authoritative sources for this, but suprisingly no. Practically everyone but the folks who are selling them advise against them, but no scientific papers or manufacturer recommendation. The most authoritative thing I could find was a passing mention from Consumer Reports:

I suspect that since undercoating is such a cash cow for dealerships, the automakers are reluctant to actually come out and say it’s unnescessary. I think maybe the most convincing thing I could say is just look around you and/or talk to older folks if you can’t remember the bad old days. In some climates new cars would start rusting within a year or two and it was not at all uncommon for cars to have serious structural damage in less than a decade. These days, even surface rust is rare unless there’s been some sort of body damage.

For the same reason many industries like that (driveway sealing, for example) exist. The people selling it can convince rubes it does some good. I’ve never had a rustproofed car, and I have never had a car rust out before it was ready for the junkyard. I live in central NY. Plenty of road salt to kill 'em, if they were going to rust.

Just to support Greasyjack via anecdote that cars in the 60’s and 70’s were rustbuckets (this probably extended to the 80’s). When buying a second hand car there were recommendations to run a magnet over panels to try and establish how much filling there was.

Today it would not be a concern for me.

A bit off topic, but the better rust resistance is a very good reason to be sure you keep up with preventive maintenance items. By the time a 60’s or 70’s car got to 100,000 miles/10 years the body was generally shot (Desert areas excepted) so there was little point in making the drive-train last much longer than that.

Many 80s - 90s cars are now being retired due to obsolete technology, and worn out drive trains rather than body rust. A decade or two back there would have been no point to a Cash for Clunkers program.

hell, I had someone grumble to me about how Chryslers are junk because her '91 Plymouth Acclaim is “falling apart.”


How spoiled are we when we expect a twenty-year-old car to have no problems?

See, they install that TruCoat at the factory, there’s nothin’ we can do, but I’ll talk to my boss.

My brother had his '76 Cutlass rustproofed by Ziebart. The only places it didn’t work was under the stupid vinyl roof and the rear bumper, which rusted off by 1990. Not bad considering how fast those cars rusted out otherwise.

Well…he never done this before. My boss said I can take $100 off of that Truecoat!