An oil is any neutral, nonpolar chemical substance, that is a viscous liquid at ambient temperatures, and is both hydrophobic (immiscible with water, literally "water fearing") and lipophilic (miscible with other oils, literally "fat loving"). Oils have a high carbon and hydrogen content and are usually flammable and slippery.

For example, `coconut oil`_, `grapeseed oil`_, olive oil. Also petroleum (?).


1   Examples

WD-40 ("Water Displacement - 40th attempt") is penetrating oil. It displaces water for rust and corrosion prevention. It was originally designed by an aerospace company for prevention rust in nuclear missiles. It's full ingredients are a trade secret. It contains a solvent.

WD-40 is a mix of lubricating oils and lighter penetrating oils. The mixture soaks in to displace water and release rust, the lighter oils evaporate, and you're left with a coating of lubricating oil over all the surfaces. This is perfect for things like hinges and sliding surfaces.

It's sort-of wrong, but it's more correct than it is wrong. WD-40 is a mix of light oils and solvents. If you spray it on a mechanism which is designed to be lubricated by a heavier lubricant like heavier oil or grease it will dissolve the existing lubricant (which is temporarily good, if the grease is dirty) and the remaining oils will not provide sufficient long term lubrication.

You mentioned hinges in particular -- it's a bad idea to spray WD-40 on a door hinge unless you follow with a proper long-term lubricant like silicone or white lithium based spray, or even a tube of grease.

When people say "it is not a lubricant" this is what they refer to. It is, in fact, not a proper long term lubricant.


You all do realize that the ingredients of WD-40 amount to kerosene and mineral oil, right? Not chemically exact, but close enough. The kerosene-like solvent evaporates, leaving the heavier mineral oil behind.

Also, it doesn't actually absorb water, it displaces it. Water is polar and so the molecules like to stick to each other. Hydrocarbons are non-polar, and so like to spread out and cover other surfaces more so than water. If a surface is wetted with water and oil is also placed on the surface, the oil will tend to spread out, drawn by a reduction in surface energies, and creep under the water, displacing it (separating it) from the surface. I could go into depth about surface energies and the thermodynamics of it, but that is essentially how WD-40 works.

Note: oil mists can be fatal to humans too if you inhale enough to coat the inside surfaces of your lungs. Still, it takes a long, long time for roaches to suffocate, so I'm guessing that the solvent in WD-40, being fat soluble, migrates into the myelin nerve sheaths, denaturing the protein component and disrupting the CNS immediately. But that's just a guess. Any insect toxicologists out there care to correct me?


But, as an engineer, WD-40 should not be confused with lubricant. It's designed to displace water, not to reduce friction. WD-40 may certainly keep water off things, and thereby maybe reduce the chances of things rusting shut or seizing, but it is not lubricant.

That said, I've heard it sometimes works, but I still think that lubricant should be used as lubricant unless its an emergency.

Lubricants are things like grease (wet) and graphite (dry).

2   Classification

Oils may be animal, vegetable, or petrochemical in origin, and may be volatile or non-volatile.

3   History

Rockefeller retired just as the US automobile industry was getting started, which resulted in him making far more money from the Standard Oil stock in retirement than in his 30+ year career before.