The trick with used oil is how is it fixed up? Could be good as new, could be not as good.
It's my understanding that a gallon of used motor oil will yield 2.5 quarts of quality used oil, since re-refining removes lighter fractional distillates, water, the former (used) additives, etc.
In general, you take crude oil and refine it to make a lubricant. This is called base lube stock. Then you have to take that base lube stock and blend it with additives in order to put it into a passenger car. That's what gives it much of its color actually. You're essentially adding an anti-foaming additive, a dispersant and a detergent.
When you put the oil into the engine, it is degraded by heat and oxidation. As all the additives start to break down, the engine starts to wear more. That puts some heavy metals into the oil. The anti-foaming additive breaks down and you start to get water mixing with the oil and making sludge. The same breakdown happens with the dispersant and the detergent. That's the reason they recommend to change it every X number of miles because of the thermal degradation and oxidation. The additives only have a certain life span.
Used oil is cleaned by using pretty conventional refinery technologies. One of them is vacuum distillation, which dewaters the oil. Used motor oil comes with somewhere between 5 and 7 percent water in it. The first thing you have to do is get the water out of it.
Then a process called wiped-film evaporation is applied to the freshly de-watered motor oil. This separates out all the contaminants and additives that are put into passenger car motor oils. Then after that, it goes through a hydrotreating process that gets up to 700 degrees Fahrenheit under around 1,100 PSI of pressure. That infuses hydrogen back into the hydrocarbon molecules and makes it a very high quality re-refined oil.
US made FP! wooo >.>
