IMG_0933.jpgKroil is an extremely effective penetrating lubricant. Almost every professional machine shop I've been in has a bottle of this sitting prominently beside the workbench. I first saw it about 8 years ago, and asked the mechanic why he used it. His words are the same I now say to those who ask me: It will unstick ANYTHING. I frequently take apart antique machinery or general equipment. There is almost always rust, grime, burned grease, metal shavings, and the wear of decades that prevent me from separating bolts from nuts, pins from holes, or keeping sliding surfaces from doing anything BUT sliding. I've used every possible penetrating lubricant on the market. Some worked OK, but nothing really was "magic" until I found Kroil. Not many products make me laugh with glee. But the satisfying twist of an otherwise impossible-to-remove bolt or the turn of a shaft that was rusted solid now make me smile because of this little orange can.
Kroil doesn't work instantly. It takes between a few minutes and a few days (for extremely large bearing surfaces) to work its magic. I once let it sit for a week on a 300 pound flywheel that was being very stubborn, and it came right off. Kroil is not for general lubrication purposes. It's very thin (which is part of how it works) and is not very sticky. But that's not the reason I use it; I use it to get things apart. Kroil has a weird creeping capability, it finds its way up and across metal surfaces like some sort of strange science fiction amoeba. After I use Kroil to separate things, I'll typically clean them completely (dip in mineral spirits) air-blast to remove residue, and then re-oil with a more permanent lubricant. The Kroil won't hurt anything if it stays, but I like to get a thicker material in everywhere to avoid having to fix the problem again in a few years. It's somewhat hard to find in a retail setting. I've never seen it in a hardware store, but that doesn't mean some don't carry it. (The label on my bottle says "For industrial use only - not for retail sale" which is somewhat antiquated.) I typically get it directly from, though eBay also might have some good deals. There are now several variants of Kroil including graphite and silicone, but I stick with the old-fashioned stuff since I haven't read the data enough on the other mixtures to figure out if it's worth changing. If someone asked me what critical items I'd want for my toolbox, this would be among them. It comes at an even higher value than general-purpose sprays like WD-40. Simply put, Kroil is the most useful lubricant I know of. --John Todd Kroil $9 Sample use: A recent example of when I have used Kroil came when I bought an Ideal #3 Stencil machine on eBay, which is used for cutting out cardboard or paper letters and numbers for making paint stencils. I purchased the machine for $40, which is about 1/5th the normal price, because the machine was rusty and jammed. IMG_0936.JPG I took the risk because I knew Kroil would work. Indeed, when I opened up the box, the rust was pretty severe. All of the vertical punch letters were rusted in place, and the dial didn't even spin at all to change letters. I liberally dosed all of the moving component interface areas I could see with Kroil, and then started to take it apart. After an hour or so of time, I was able to get all of the moving components back into fully operational condition after slowly working them through a few gritty and then progressively smoother cycles with the Kroil finding its way into the nooks and crannies. IMG_0937.JPG Even the central shaft which was frozen solid with several hundred pounds of turning force, after two hours or so I was able to feel a little movement, and after another hour and some huffing and puffing I was able to get the assembly off the shaft. Don't forget to comment over at Cool Tools. And remember to submit a tool!



  1. Half and half automatic transmission fluid and acetone works just about as good as Kroil, at one heck of a lot lower price per ounce.

    And those two components are easy to find at retail.

    (Cribbed from the web bit follows)

    “The April/May 2007 edition of Machinist’s Workshop did a test of penetrating oils where they measured the force required to loosen rusty test devices. Buy the issue if you want to see how they did the test. The results reported were interesting. The lower the number of pounds the better. Mighty interesting results for simple acetone and tranny fluid!

    Penetrating oil . Average load .. Price per fluid ounce
    None …………….. 516 pounds .
    WD-40 ………….. 238 pounds .. $0.25
    PB Blaster ……… 214 pounds .. $0.35
    Liquid Wrench … 127 pounds .. $0.21
    Kano Kroil …….. 106 pounds .. $0.75
    ATF-Acetone mix.. 53 pounds .. $0.10

    The ATF-Acetone mix was a 50/50 mix (1 to 1 ratio).”

    1. Kroil has a very high flash point. So you can pour it on and hit the exterior part with a torch to help with the separation. Not something you do with the atf/acetone mix. “Better” depends upon circumstances.

      1. Anonymous “…and power steering fluid (NOT automatic transmission fluid).”
        Same fluid, different bottle. Not in all cases, but my previous car used ATF Dexron II for the power steering.

        1. During my days of owning only Murkan cars, I did the same, but my Honda requires “genuine Honda power-steering fluid”.

  2. Kano’s “Floway” is the bomb for real. Good stuff. WD40? No match. They make good products.
    (I don’t work for them!)

  3. I personally swear by a 50/50 mix of ATF and acetone. I normally use plain Dextron/Mercon, but anything from Type F to Pentosin works.

    Kicks Kroils butt at the cost of being hard to keep around. Crap plastic container? The acetone eats it away. Seal the container badly? All the acetone evaporates.

    1. Thanks so much. I was already thinking I’m the only one in whose mind this sentence kept echoing.
      However – it can never hurt to have plenty of good penetrating lubricant, so thanks for this post. But is it really dermatologically tested?

      1. You’re no the only one at all. And remember, he’s tried every one on the market!

  4. I have never understood those who try to use WD-40 as lubricant. Do they not realize that the WD stands for Water Displacement?

    1. Just a guess, but it’s probably because it can be used as a lubricant. Says so, right on the can.

    2. WD-40 isn’t formulated as a lubricant, but will act as one. So long as there is no appreciable load. Or speed. Or any particulate. In short, if your application is on a home sewing machine’s thread spool axle, it’s fine. It’s not fine for the sewing machine’s internal components (as a lubricant for operating the machine. For cleanup, it’s ok).

  5. I’d almost forgotten about good old Kroil. I had a can of that stuff a few years ago, when I was working on my old ’68 Ford Custom. Kroil is good stuff, but I think it’s worth mentioning that most people won’t need it unless you do a lot of metal fab or restoration work (which is what the review is suggesting, anyway). If you’ve got an old car to pull apart, Kroil can be helpful.

    Nowadays, the most I need oil for is on the drill press and a few small parts. For that, 3-in-One, WD-40 or Liquid Wrench is fine.

  6. I appreciate learning about the ATF-Acetone mix. For someone who has a large work area with many components, it’s probably the right choice.

    But for me, I’d rather have something small and easy that costs a bit more per ounce than something that requires multiple caustic ingredients and special storing. Price is not my deal-breaker in a situation like this.

  7. I use Krull for all my disassembling needs. I just play the DVD and everything falls apart.

  8. Ok, I am sold. I have a classic Jag that has plenty of rusted bolts and parts, and this looks like it could do the job. Also, in regards to WD40… You guys are right. It doesn’t do the job very well for very long. Growing up we had the “oiling can,” and it was much more effective and long-lasting then the WD.

  9. In regards to the ATF (or automatic steering fluid as stated – BTW, which one?)… I could be very wrong, but I am not sure if that would be very good once in contact with skin. Dangerous.

  10. doesn’t steering fluid eat through a lot, i mean if you had any non metal, nylon washers etc, or painted parts it could be bad

  11. As a marine engineer I work with the MOST rusted fasteners. My preferred method is to heat with an Oxy-acet. torch and the apply aero-kroil. It is twice the price of regular kroil but it kicks major butt.

  12. is it me or does anyone else feel like they are reading a j. peterman catalog for cool tools

  13. Diesel fuel is also a fairly effective penetrating oil, and it’s cheap enough to use for soaking large parts.

  14. I was traveling on business and got a late call from my wife. She was frantic that our daughter had gum or some other sticky stuff stuck in her hair. I directed her to the bottle of Kroil in the garage and the problem was solved :)

  15. I have used aero-kroil and I bought a gallon just because I did not want to run out.
    I use is when I need it when nothing else works.
    I got some old 8 ton screw jacks(rail road supply) that were frozen and had been that way for a long time I soaked them for over a month and they have been restored to working condition.
    It is not for everything but when you need it it delivers wait a while and low and behold it is loose.

    uncle frogy

  16. excellent for artists and paint tops…acrylic and oil..a tiny bit on the threads of the top and the paint never sticks…awesome…

  17. I normally used 2 stroke oil it works and is cheap. The advantage of wd-40 is the aerosol can which makes it easier to get at difficult to reach nuts.

  18. Marvel Mystery Oil – my grandfather used that for about everything. You can still get it at auto parts store as a fuel additive. Light oil, ruby in color, smells nice. Use it on oilstones, as cutting oil etc etc.

  19. kano kroil is also often used for a lubricant for target shooting. This might be where you can find it as its used to clean rifle bores and lubricate…

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