- Lubricates noisy door hinges on vehicles and doors in homes.
- Lubricates and stops squeaks in electric fans.
Bullshot Crummond. In both of these instances, in my own experience and that of other people I've known, this is only true very temporarily. My father destroyed the door hinges on my car because, unbeknownst to me, he was hosing out my door hinges with WD40 every time I came to visit. I kept regreasing my hinges, not knowing why it kept disappearing, but WD40 washed out all traces of the grease and got them grinding again. After around a year of this (I don't know when he started doing this), I could only close the driver's side door if I lifted it up.
I've used it to lubricate squeaky door hinges, only to later have them get even worse. A couple drops of 3 in 1 oil fixed it.
I tried it on some stiff fan bearings. Sure, it clean them out, but left them basically dry. In a relatively short time, they started squalling. A little 3 in 1 oil extended the life. For those fan bearings, I've found a good light spray cleaner to work well, let dry, then followed by a few drops of 3 in 1 or sewing machine oil.
I've repaired electronics that people have sprayed WD40 into. Pots that have seized up, sliding pots especially. Cassette decks with swollen rubber and no oil in the bearings. VCRs that stink of WD40 because someone just opened the door and hosed it down due to a squeak, or because someone told them to clean their VCR heads that way.
It has its uses, but a lubricating oil it is not. It bugs me when people treat anything as a panacea.
BTW, if you have someone working on your furnace or ducting and you see them using cloth fabric "duct" tape (actually duck tape) on it, fire them on the spot because they don't know what they are doing. Hire someone else in, ask to see his/her roll of duct tape. Only if it is actual aluminum tape, have them check the other person's work and complete the repair.
What everyone calls "duct" tape is really duck tape, invented to make quick, temporary waterproof repairs to things like ammo cans and such for WW2. As anyone who has ever used it on anything outdoors knows, it breaks down quickly in heat and cold. As anyone who has used it or had someone else use it to tape down an extension cord knows, it becomes this sticky mess that is nearly impossible to entirely remove. That's why roadies use gaffer tape, even though it is much more expensive.