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We recently found something interesting at Brownells gunsmithing supply — they tested how well a number of substances prevented rust.  The results surprised us:  Plain old WD-40 was the most successful in keeping rust from forming on a mild steel surface, outperforming many other substances engineered specifically the job.

So what do you think, Hot or Not?  Let us know in comments.

Knowing the Limits of Rust Preventatives [Brownells]


22 Responses to Hot or Not? WD-40 For Rust Prevention

  1. mark says:

    Doesn’t WD stand for water deterrent. Sounds like it’s doing what it’s designed for.

  2. Gordon says:

    I vaguely remember another study showing T-9 to be best. I’ll see if I can find the web site or reference.

  3. ToolGuyd says:

    WD-40 is excellent for water displacement. I never would have expected it to last as long as those experiments describe. I would have thought that the steel’s exposure to “scorching heat” and “horrific thunderstorms” would have cleaned most of the WD-40 off of the steel.

    Is anyone up to running a copycat test?

  4. Chuck says:

    Better than Cosmoline? The Russians had it wrong?

    • Papa Karlo says:

      That’s funny! Russians have nothing to do with Cosmoline, they use what they call gun oil and cannon grease, both have their own recipe. Cosmoline just resembles the Soviet gun grease, but its ingredients are totally different.

  5. bs says:

    YEA, some of that stuff is pretty expensive. I like to use wax on my table saw. its in the barn and during temperture changes a lot on humidity can condensate on it. Just plain old parafin or an old candle. clean the rust off first then apply wax. makes it sliperry too.

  6. Dave says:

    What, no test of Ed’s red?

    (google it- it’s a home-made freeing oil recipe)


  7. Mike P. says:

    WD-40 did very well, but if you read the article, it was not “the most successful”.
    “Rig Universal Grease” was the best (“No evidence of rust formation or discoloration. The degreased plate shows the metal is unmarked.”) WD-40 results = “Minimal rust formation is present; almost no pitting is visible after degreasing.”

  8. Gordon says:

    The article I was thinking about was in Wood Magazine, March 2004, which compares 14 products for rust removal and prevention. T-9 won. http://www.woodstore.net/rustbusters.html

  9. Toolhearty says:

    Gordon: Link goes to $3 pay-per-download catalog page.

  10. Gordon says:

    Toolhearty: try this link http://www.boeshield.com/index.htm

  11. Ron says:

    WD-40 (water displacement formula #40) was developed by a fellow at General Dynamics in San Diego for the Atlas rocket, which had an all stainless steel structure at the time.

  12. diluded000 says:

    I wonder how paste wax would have fared in this test. I use it on my cast power tool surfaces several years ago, and they don’t have any rust. But I live in a really dry climate.

  13. Joe says:

    Dave–thanks for the Ed’s Red tip–it looks like a good ‘un. Coincidentally, I’ve used ATF in the past and it’s worked well (it was “available”). And since WD40 is largely kerosene, that’s not a big surprise to see.

  14. Barry says:

    I vote not…

    WD-40 displaces water for a short period, but dries out in a few days.

    • Otto says:

      I did my own test WD 40 BreakFree clp,Gear Lube Oil and Remoil.
      After one week the only steel plate not rusted was treated with WD 40.

  15. Joel says:

    @ Joe:

    I’ve always wondered about how ATF would fare in a trial like this. That stuff is damned sticky, and coats well, and doesn’t seem to wash easily.

    I’ve read that phosphorus can be a big help in rust prevention, and that the common formulations of chainsaw bar oil make an excellent rust repellent/inhibitor.

    I don’t know how either ATF or CBO would work on a gun…

  16. Bren R. says:

    I use Ed’s Red as an immersion solvent for gun parts. It works very well, leaves a nice thin coat of ATF (which acts as a lubricant and rust preventer). The only problem is it stinks to high hell.

  17. shopmonger says:

    WD is great after you wash tools to “Displace water” then use another lubricant to “save them” if you are planing to store them for a long period of no use….

    other than that for cast iron waxing is the way i keep my tools in goods condition

  18. JAMIE says:


  19. Stig says:

    Hi, we tested WD-40 on one mild steel shim plate placed unprotected on a factory roof here in Norway, another plate was covered with a professional product, the last one left unprotected. The environment was very low ph, lots of so2 in the air, and rain..
    After 12 months the two first plates was barely rusted, the unprotected one heavily rusted and useless.

  20. Paul Gerhart says:

    Have used WD-40 for years to displace water, and to stop and prevent rust. (WD stands for Water Displacement. I believe that the 40 comes from being the 40th mixture that was tested while the product was being developed.) Once the volatile components evaporate, it leaves behind a very heavy, non corrosive, oil that tends to prevent rust. Spray it on a mirror, and see what’s left after 2 days or so. It works well on automotive connectors in climates that use “salt” on the roads. Have even used it on printed circuit boards as a “postcoat” to prevent corrosion. It is non conductive, is easier to remove than postcoat if repairs are needed, and flows everywhere, unlike most postcoating materials. For rustproofing, it’s hard to beat. As a lubricant, it’s OK if what you want (when it drys) is a very heavy oil. It’s OK for things like door hinges, not so hot for electric motors, etc.

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