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According to this answer WD-40 is not a true lubricant. I don't get it - even Wikipedia says

The long-term active ingredient is a non-volatile, viscous oil which remains on the surface, providing lubrication and protection from moisture.

which sounds quite solid.

What exactly does WD-40 lack that prevents it from being a true lubricant?

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A side note, just because wikipedia and\or marketing material says so, doesn't mean its true. –  Web Jun 1 '11 at 12:57
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The "WD" is short for "Water Displacement". No citation but if I remember it was used to get water/frost off and keep it off of space vehicles originally. –  Mark Schultheiss Jun 1 '11 at 14:31
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2 Answers

up vote 18 down vote accepted

WD-40 is composed of many different chemicals, and only about 10-20% of these are lubricants. Even then this small amount is only a very light mineral lubricant. Most of the other components are intended to help penetration, but are volatile and are intended to evaporate.

WD-40 does provide some longer term lubrication, but the problem is that the volatile components will dissolve and displace whatever lubricant already existed (e.g. grease), and then the majority of the WD-40 will evaporate. So really it should not be used on anything that requires propper lubrication (or at least, a proper lubricant should be added again some time after using WD)

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Would that include Bicycle gears and wheels? –  JL01 Jun 1 '11 at 12:30
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@JL01: Definitely - the chain contains grease behind the seals on each link, you should only use bike chain lube. Wheels too -anything that has bearings (wheels hubs, crank bearing etc.) shouldn't be doused with WD - if you do your bearings will wear out in no time. –  UpTheCreek Jun 1 '11 at 12:51
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Do not use WD40 as a lubricant on bikes. For cleaning, yes. –  Zepplock Jun 1 '11 at 18:44
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Looks like we can finally put this tired disagreement to bed, so to speak:

enter image description here

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+1 -Says it all. –  SteveR May 22 '12 at 16:45
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