Originally Posted by
cyccommute
You won’t use WD40 because it is ”weird and waxy” but you’ll use automatic transmission fluid which contains all kinds of extra additives and is meant to be used in a sealed unit. ATF and motor oil were never designed to be used in open air systems.
WD40 isn’t weird and waxy. It is just solvent with mineral oil in it. The mineral oil is in the same class and of a similar composition to the oil used in TriFlow, 3-in-One oil, or any commercial light mineral oil. Even Phil Tenacious Oil contains the same class of oil and even a similar molecular weight range. The oil is what makes WD40 such a crappy solvent, it’s the residue that it leaves behind. It’s now better but also no worse than any mineral oil that might be used for this application.
If you're going to argue that ATF shouldn't be used as a lubricant because it was designed to be an application-specific hydraulic fluid, you don't get to argue that WD-40 should be used as a lubricant or a solvent, since it wasn't designed to be either. WD-40 was designed to be a water dispersant (hence the "WD") and rust preventative, for use as a surface preservation treatment for ICBMs. (Airman Schmuckatelli had to apply it to the outside of the missile with a mop.)
Of course, it turns out that both of these things can be used outside the applications for which they were designed, because, as you said, light oils are fairly interchangeable, especially in extremely low-stress applications. Like, for example, the <0.5 HP power, <500 rpm environment of a bicycle drivetrain. All anyone is saying about Water Dispersant #40 is that it's not ideal for the applications under discussion, and that there are better choices.
Which there are, because it isn't.
--Shannon