I see it listed under free stuff in CraigsList, and it seems to always be taken. I have about 6 gallons of the stuff that I’d rather not lug to the recycler if someone would rather pick it up. Or is it just one of those CL phenomenons, that if it says ‘free’ it is as good as taken.
There are many old wives tales about using old motor oil. For example, I’ve seen dogs with skin disease slathered in old motor oil. Bleech. Many of the old wives tales specifically recommend “burnt” used motor oil.
Some shops have heaters that can burn this stuff. It’s thus replacing approximately the same quantity of (expensive) home heating oil.
When I used to live in a house with oil heat, I dumped my used oil and that of friends/family in the tank. It only amounted to just couple gallons or so over a season; in such a low concentration–it was a 250-gallon tank–it causes no problems with the burner. Although it’s not saving much (what, 10 bucks, maybe?) it was a convenient means of getting rid of the stuff.
It’s also used as a sealant/preservative for wood that will be outdoors. Wooden pickup truck beds are not made of pressure treated because the weight is much more than regular 2x spruce. This lumber would only last a few years without being treated, and motor oil is a free waste product that does the job as well as thompson’s water seal, etc.
Companies such as Safety-Kleen pick it up from the Quicky Lubes and recycle centers and they recycle it. They filter out all the crud that made it old. They test and adjust the viscosity to a standard point. They put back some additives that your engine used up. Then they resell it.
Who buys the reconstituted oil? I don’t know that part.
Another place it goes is to fly-by-night driveway coaters. They apply the used oil instead of real driveway coating stuff. By the time the sucker gets wise to the game, the scammers are long gone.
A friend of mine who made Medieval armor for SCA usage would quench heated metal in used motor oil. Not sure what the point was, but it was nasty smelling. Hehehe
Hopefully someone more knowlegeable than myself will be along shortly, but it has something to do with the carbon content of the steel. It makes it more durrable.
I thought that was blood, not motor oil.
When I was a machinist we would quench certain steels in oil because it cools the metal less quickly. Water vaporizes easily and has a high heat of vaporization, carrying the heat off in a hurry. The steam can also form a barrier that prevents the water from reaching internal surfaces. Oil does not vaporize as readily, and stays in contact with the part giving more uniform and slower cooling.
I would not use motor oil for this purpose. Used motor oil contains wear particles from the engine. You can pick up considerable nickel and chrome in used motor oil, and the fumes given off might not be good for you. The same goes for burning it in a heater at home, although a larger unit with a precipitator would scrub the metals pretty effectively.
Quenching in oil changes the grain structure of the carbon in the steel. I believe that this has the effect of more evenly distributing the carbon throuhout the steel. Making it more impact resistant.
My grandfather used to smear “burnt” oil on his hogs. He said it kept the flies from biting them.
That sounds bad. Doesn’t used oil have heavy metal and stuff in it?
Maybe that’s the secret to BBQ in your part of the country. That’s a new one on me. 
Quenching in oil cools the steel more slowly than, say, water. Many types of tool steel are specified as oil-quench steels such as O-1. Some other types of steels are too such as 5160. Quenching them in water can cause them to crack. There are special quench oils for this sort of thing, but I have certainly seen blacksmiths use used motor oil for this. I know about the fire danger, but I wasn’t aware of heavy metal problems. Presumably, the particles are too big to be vaporized by the hot steel (which is also probably not even hot enough to vaporize lead although I don’t know the B.P. off the top of my head) and the things that smiths are quenching are things like knives and woodworking tools where I wouldn’t expect the presence of the metal particles to make a real difference.
FWIW,
Rob
Where would the heavy metals come from? Lead isn’t a significant component of engines anymore AFAIK, and I don’t think that cadmium is that big of a component of the internal workings of an engine.
BTW, used motor oil makes a good lawn fertilizer.
We are planning to fix the doors on our 100-year-old tobacco barn. The building’s lumber has completely grayed and weathered, and we love the look of it. We’ll be using unplaned lumber from the saw mill for the new doors and jambs. And we’ll be painting them with burned motor oil, which will leave them practically matching the rest of the barn.
The significant metals of interest in used motor oil are nickel and chrome from bearings and bearing surfaces. I used to test used motor oil for someone who burned it in a large industrial furnace with proper precipitators. Their threshold for rejection was 1000 ppm chrome, and I used to regularly reject oil for being higher than that.
Tuckerfan,can you give a cite for that closing comment,
“BTW, used motor oil makes a good lawn fertilizer.”
There’s a group that I’m not supposed to talk about which says that.