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Looks like WD-40 can be used for lubricating just about any metal parts.

Are there non-obvious cases where using WD-40 will be harmful to the stuff lubricated?

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35  
Don't combine WD-40 and Duct Tape, you risk creating a black hole. –  Adam Prax May 10 '11 at 16:00
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A lighter seems to be a bad idea to "lubricate". –  Spechal May 11 '11 at 4:46
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Also, it's not for ... personal use. –  Jay Bazuzi Mar 11 '12 at 1:10
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By the answers given, it's clear that you asked the exact opposite question of the one you should have asked, to wit: "When should I use WD-40?" So far, we've learned that it's not a lubricant, it will attack plastic, lacquer (insulation on magnet wire in a motor), etc. It's really just for cleaning water off of things, and happens to work as a weak penetrating lubricant. It's kind of like a Swiss Army Knife in that you could use it for all sorts of things, but you really shouldn't. Use the proper lubricant for the job and you'll be happier in the long run. –  Andrew Beals Mar 12 '12 at 19:09
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Perhaps this will help: i.stack.imgur.com/EzXXb.jpg –  oscilatingcretin Mar 14 '12 at 18:13

17 Answers 17

up vote 39 down vote accepted
  1. Firearms - you should never use WD-40 to clean or maintain firearms. It's hygroscopic and will attract moisture to the firearm which will result in rust.
  2. Drive chains of any type - because WD-40 isn't a lubricant it really will not work well on Drive chains of any type.
  3. Gears of any type - WD-40 doesn't have enough lubrication affect to be useful on any type of gearing. only specified gear lubricants should be used.
  4. Locks. Use powdered graphite or silicon spray instead.
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1  
WD-40 is a lubricant. –  xpda Mar 17 '12 at 15:15
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No it's not, really. See other answers. –  tomfanning Mar 18 '12 at 21:51
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@tomfanning "WD-40 cleans/degreases, penetrates to loosen up stuck parts, prevents corrosion and is a light lubricant." wd40.com/faqs There are several more mentions of WD-40 being a lubricant on the site. It contains mineral oil, which is a light lubricant. –  xpda Mar 19 '12 at 4:08

WD-40 isn't actually a true lubricant. WD stands for water displacing. The main use for WD-40 is as a solvent and a rust dissolver. The lubricant-like properties of WD-40 are from rapidly evaporating components. It won't last. True lubricants include things like silicone, grease, Teflon, graphite, etc. WD-40 can be good as a first go at things, it can help clean up rust or other grime and then you can apply your lubricant.

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21  
+100. WD-40 is NOT a lubricant. It will help free up stuck joints and penetrate into them, at which point you can now apply real lubricant of some kind. –  Alex Feinman May 10 '11 at 16:51
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WD-40 is a lubricant. –  xpda Mar 17 '12 at 15:15
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@xpda When the person on the other side of the issue has given more information than you, your comment is very unhelpful. Have any references for that? –  NickC Mar 18 '12 at 17:10
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@NickC "WD-40 cleans/degreases, penetrates to loosen up stuck parts, prevents corrosion and is a light lubricant." wd40.com/faqs There are several more mentions of WD-40 being a lubricant on the site. It contains mineral oil, which is a light lubricant. –  xpda Mar 19 '12 at 4:05
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Just because it contains a small amount of lubricant does not make WD-40 a lubricant itself. It contains many other solvents which counteract the lubricating properties of the mineral oil such as acetone. –  Cody C Mar 30 '12 at 15:24

WD-40 does a lot of things, unfortunately this means that it does not do any one thing well.

As a lubricant WD-40 is very thin and runny. WD-40 will lubricate for a short time, but will quickly run off. This is a side effect from it being a penetrant. If it was thicker for better lubrication it would not penetrate well.

WD-40 is a GREAT quick-fix and one-can option. I use it in that role, it gets things going long enough to let me finish the current task and get back to the shop. Once there I can get to my real penetrants (Kroil, PB Blaster) and my real lubricants (oil, white lithium) and repair the problem.

Bonus tip: wrap your WD-40 can with several turns of duct-tape. You now have two of the best quick-fix wonders in one package.

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2  
And WD-40 is really good at cleaning away whatever little you may have left of a previously applied thicker lubricant. –  Vebjorn Ljosa May 10 '11 at 23:17

Never use WD 40 on door hinges or anything you want to keep clean. It attracts dirt and dust. It will turn your hinge pins black.

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8  
What would be good for door hinges? –  Paul D. Waite Jun 1 '11 at 14:33
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This is also the reason you do not ever use it in locks, especially pin tumblers. My brother (a locksmith) used to swear at people who tried to "clean" a tumbler with WD-40. And he's not a sweary person. –  staticsan Mar 9 '12 at 2:11
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@PaulD.Waite A very light oil is good for hinges. a common brand is called 3-in-1 Oil. While not as easy to apply, vegetable oil (the kind used for cooking) will work and you can even get it in a spray can (brand name Pam) but don't get the kind with flour or flavoring. –  Christopher Estep Mar 9 '12 at 22:35
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3-in-1 oil will attract dirt and dust just as bad as WD-40. And for matter, so will any other type of oil or grease. For locks you can use graphite powder, for door hinges the natural polishing action of using them is enough. –  Jonathan Allen Mar 17 '12 at 7:10

It doesn't move and it should = WD40
If it does move and it shouldn't = duct tape

WD40 is only used as an immediate lubricant, eg. for a stuck bolt, or a s water dispersant. Don't use it where you need longer term lubrication, like a bike chain.

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ah, the old roadies' motto. There was a third case, but it's not safe for this site. –  Agos May 11 '11 at 8:54

Rubik's cubes. Serious cubers will lube their cubes with Jigaloo, CRC silicone, or even vaseline. But, will point and laugh at noobs who use WD-40, as it melts the cube, likely seizing it. Yet people keep doing it.

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4  
WD-40 contains petroleum distillates (e.g. Paint Thinner), which can break down certain plastics. –  msemack May 16 '11 at 13:15

Bicycle chains!

WD40 will ruin a bike chain and the gears wear out quicker. It washes the dirt in, the dirt acts as an abrasive and not a lubricant.

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Try grease or heavy gear oil, that will really attract dirt. I like WD-40 or 3-in-1 oil for my bike specially because it doesn't last. –  Jonathan Allen Mar 17 '12 at 7:12
    
WD-40 will not ruin a bike chain. It will loosen up a rusty chain. Rust and dirt will ruin a bike chain. However, wax or teflon lubricants will keep a bike chain cleaner (and you can go faster). –  xpda Mar 17 '12 at 15:18

Musical Instruments.

My sister works at a music store, and a father ruined an $800 clarinet by using WD-40 on "the squeaky part".

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17  
Off-topic, isn't the whole clarinet "the squeaky part"? –  Freiheit May 12 '11 at 18:52
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@Freiheit - only when you're starting. :p –  AnonJr May 12 '11 at 18:59
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As a clarinetist, this makes me cry. And @Freiheit, as a clarinetist, that made me laugh. –  Fred Larson Jun 20 '11 at 18:58

Personal experience: An electrician told me never to squirt WD40 into an electric motor (bathroom exhaust fan) as it can be ignited.

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Duh, so will any oil. –  Jonathan Allen Mar 17 '12 at 7:14
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Light oils will. Motor oil won't. But it's hard to get motor oil up there. –  xpda Mar 17 '12 at 15:20

Lock cylinders. Never in lock cylinders. Doorknobs, padlocks, etc. - the residue left will just attract dirt & grit, and prematurely wear down the works.

This was given me by a college friend whose dad worked on the maintenance staff - so they did a lot of locks!! It probably took years to see the pattern, but any lock they had shot with WD-40 eventually failed before un-WD'ed locks.

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For that matter, don't use any sort of oil on locks. If you have to use anything, use graphite powder. –  Jonathan Allen Mar 17 '12 at 7:13

I read an article once by a clock repairman who described how bad WD-40 is for precision clockworks. The main reason has been given already: it attracts dirt, which acts as an abrasive and eventually gums up the action.

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It never should be used on AirSoft or PaintBall weapons as it melts the seals.

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For something where you need longer lasting lubrication, consider Silicone-based spray. Comes in a can just like WD-40, but it "sticks" better.

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It attacks polycarbonate windows such as Tufak or Lexan too. Shooting through a bullet proof window after applying is NOT recommended.

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Good advice! WD-40 will make it tough to see through a polycarbonate window. –  xpda Mar 17 '12 at 15:20

Don't ever use WD-40 on something that has already been lubricated (like with white lithium grease, etc). The WD-40 will break down the grease and make a real mess.

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For the same reason you wouldn't use it on door hinges, it should never be used for chair and sofa mechanisms. Because WD-40 attracts dust and turns things black, over time that dirt accumulation within the moving parts will build up and eventually start to fall off onto carpeting creating a terrible black mess that is nearly impossible to remove.

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Any electric motor, even if the rotor is stuck from filthy dried-up lubricant! Think squeaky furnace blower motors, fans that won't start up, lawn mower engines, etc.

The solvent not only removes any remaining lube, but it can melt coil wires (the lightly-coated copper wires twisted up in electric motors) and cause an electrical short. New fan motor! $200!

I did use it to help start a snowblower, which worked well for 1 use, then never ran again (likely due to WD-40's hygroscopic nature). There ARE, apparently, OTHER WD-#'s

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protected by ChrisF Mar 17 '12 at 22:28

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