Review: 3M Rust Preventer Spray

Despite the mild Midwest winter that I’ve enjoyed mostly bottled up in my house writing, I’ve noticed an ever-expanding problem on my daily driver: rust. While I’m not particularly inclined to think twice about it, I intend to keep the car until it ceases to be and would like to preserve it a little. I fully intend to (learn how to) repair it correctly, but I thought I’d see first if this 3M Rust Preventer could help slow the conversion of car to iron oxide.
[Editor’s Note: 3M™ sent us this product to test. We didn’t tell them how rusty our cars already were.]

The car in question is my 2004 Ford Focus ZX3. Having survived a dozen Midwest winters, the underside has begun to look like a shipwreck artifact, but only recently has it crept openly into view. I took this medoicre photo late in the summer of 2016; you can see the visible rust at the bottom of the door.

Ironically, the Focus likely has too much rust for a “preventer” to make much difference; the info I got from 3M recommends its use on new cars and recently repaired ones to keep rust from seeping into the body panels. That said, I thought I’d see (A) how easy it is to work with and (B) if it could perhaps slow the oxidation process.

The box comes with a single 12-ounce can, a nozzle with one clear spray tube, and three additional clear spray tubes. The idea is to connect the tubes to the length needed to reach deeply into body panels and crevices. You slidethe correct-length tubes—which can reach about three feet—into the area, depress the nozzle, and steadily slide the tubes back out to coat everything evenly.

Knowing the Focus’ doors were the worst of it, I looked for a logical entry point. There is a nice easy drainage notch at the bottom, so I followed the prescribed procedure. The connected tubes held together nicely and after aligning the can to a usable angle, the nozzle let me put down a nice foamy spray inside the door panel.

I followed that up with some spraying under the rubber door insulation, where the corrosion is pretty bad. I don’t expect miracles, especially because I applied it in 35-degree weather, but even a bit will help. The directions recommended two to three applications, so I waited an hour and then sprayed some more inside the door. Obviously, I won’t know if it makes a difference for a long time, but it was easy enough to use that when I repair the rust correctly, I’ll top off the repair with a shot of the Rust Preventer to keep it from corroding all over again.

Living in the Northeast has its perks, among them the dynamic beauty of the changing seasons. Yet winter has a major downside for us car lovers: road salt. While the snow may create picturesque scenes and an irreplaceable charm, it inevitably means that the plow trucks will be out dumping ice-melt and road salt to make the roadways less slippery and less dangerous. And though road salt may mean the saving the lives of many cars and people, it in turn poses a negative side effect on the cars themselves: rust.
To help quell the devil disguised as a chemical process that eats at our beloved vehicles, 3M is here to help with their Rust Preventer Spray. The spray-on product was designed to stop rust, and eager to prevent it from spreading to un-harmed areas of my 4Runner, I took precaution and set 3M’s Rust Preventer Spray to work.

The packaging itself it is simple and easy to decipher, with the instructions laid out on the box for quick access. One nitpick is that the directions were somewhat lacking in details, but not to the point of it harming the overall quality of the product.
There’s little I can say about the usage procedure that Eric hasn’t already said, but I’ll reiterate that the spray is extremely straightforward to use and, for what it claims to do, takes very little time to achieve those results. In order to use the Rust Preventer Spray, you simply shake the can for one minute, assemble the straws, place the cap onto the top of the can, and spray the contents into the location in which you’re hoping to prevent rust.

Whether the product is in fact capable of preventing oxidization isn’t something that can be determined on a visual level over a few days, but rather over years. As such, I cannot attest to whether it successfully lives up to its long-term claims being that it’s only been on the 4Runner for a few days.
So while I might not be say whether 3M’s Rust Preventer actually accomplishes what it claims to do, I can praise the ease of application and the ambition. And while that may not be the most important aspect of a product that claims to prevent a natural harm on one’s car, the fact that the Rust Preventer is easy to use and promises significant results for little money and effort might be worth the try for anyone looking to increase their car’s longevity. If 3M’s Rust Preventer product does in fact work as advertised, it’s a dream come true for cars of the Northeast.
[Photos: Eric Rood, Ross ballot]

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7 responses to “Review: 3M Rust Preventer Spray”

  1. P161911 Avatar

    So is this stuff think when it dries or a thin film or even visible? Don’t need it for a car, but might be good for tools and some boating stuff.

    1. The Rusty Hub Avatar
      The Rusty Hub

      It is still visible when it dries. A bit like a spray foam.

  2. Alff Avatar

    Given that rust typically forms in inaccessible areas, I see limited value here.

  3. SlowJoeCrow Avatar

    Seems like their take on the British standby Waxoyl. Since I live in a place with a dryish climate and no road salt I’ll pass for now.

  4. 0A5599 Avatar

    Doesn’t it work best when the original owner of your car sprayed it on long before you bought the car? How do you make that happen?

    1. ptschett Avatar

      Gosh, I am the original owner of my ’96 Thunderbird and needed something like this about 9 years ago. (I didn’t expect the rocker panels to rot from the inside out.)

  5. Sjalabais Avatar

    I read “rust preventer” and my right eyebrow jumps. Can’t control it. I didn’t really get it from the text, but did you spray one side and leave the other open? So that after 2-3 years, you can see the difference?
    In my neck of the woods, there are essentially no new cars that have not received an undercoating with Tectyl, Mercasol or the kind. This needs checking and refreshing every 3-5 years. Earlier, just spraying a mix of diesel and oil over the undercarriage used to be very common, but obvious environmental concerns put an end to it. When it comes to those “empty spaces” in doors and frames etc, I just spray WD40 into them occasionally, but you will also have to clean them regularly. They’re, after all, meant for drainage, too. Foam sounds cloggy, and wouldn’t be my first choice.
    Tl;dr: Sceptical 11/10, not yet convinced.