There are many benefits to frequently changing the oil in your vehicle. This is why the vast majority of people simply drain it, replace it, and recycle it. Still, what if you could reuse old motor oil? And if so, how? Although technically possible, it requires professional re-refinement to fully restore the oil’s effectiveness and bring it back to original quality standards. According to the Washington State Department of Ecology, only API-certified re-refined oils will be approved by automakers.
This means that unless it has been professionally and thoroughly processed, it simply is not suitable for reuse in a car engine. Studies have also shown that, after the oil reaches a certain mileage or age, it rapidly loses its effectiveness, becomes thinner, less stable under heat, and more volatile. Ultimately, if you just pour used oil straight back into the engine, you will likely void the car’s warranty and shorten the engine’s lifespan.
The process of industrial motor oil re-refinement includes removing the contaminants from the oil, stripping away all of the degraded additives, and recovering the base. According to the Texas Transportation Institute, the motor oil re-refining process typically includes “three distillation stages, followed by a hydrotreating process.” First, the oil needs to be heated up to 275 degrees Fahrenheit, which allows for the removal of water and light fuel.
Next, the oil goes through an atmospheric distillation unit that further heats up the oil, getting rid of lighter hydrocarbons and contaminants. The third re-refinement stage is called vacuum distillation, and it includes separating the usable oil base from sludge and various metal residues. Oil is then hydrotreated to remove the last of the contaminants, making the base oil comparable to virgin oil. With all of the proper additives added, oil is then blended before it undergoes certification processes to meet API and SAE standards.
Once that is done, the oil can be sold and used for engines. It’s also important to note that re-refined motor oil and recycled motor oil are not the same, as recycling isn’t as thorough a process. Recycled oil may not be as good as new or re-refined oil, but it does serve plenty of useful purposes as marine fuel, industrial boiler oil, or other non-engine applications.
Gone are the days when people used old motor oil to start fires or kill weeds, since these practices are dangerous and often illegal. Motor oil is toxic and it can contaminate the air, the sea, and the land. According to the U.S. Environmental Protection Agency, “used oil from one oil change can contaminate one million gallons of fresh water — a years’ supply for 50 people!”
The reality is that the only safe way to handle used motor oil, without industrial equipment and a chemistry degree, is to take it to a recycling facility. Be sure to do your homework and check how to dispose of engine oil safely. This means that, even if you thoroughly filter the oil via an oil filter before reusing it, this process will not get rid of any of the smaller particles. Only a thorough re-refining process can restore engine oil to its original properties. The overall acidic profile, toxic additives, and smaller contaminants can still wreak havoc on your engine, your health, and the environment.
All in all, although reusing old motor oil may seem like a great way to save money, time, and the environment, it often ends up being the opposite.