Frankly from what you are saying, I'd be more concerned about the gasoline than the used motor oil. Ryder Truck Rentals have for many years pumped the used lubrication oil from an engine, filtered it, and blended with fuel then pumped back into the fuel tanks of the unit it came out of. Several other of the larger freight delivery companies use a small blender which injects engine lubricating oil into the fuel system, while operating. They never change the oil, just add make up at each fuel stop, and change the oil filter. Believe me when I say neither of these companies would do this if their engineers and tests from prior years were not extremely positive in results.
If someone has a means of pumping oil through a decent filtration system, then allowed it to settle, I would have no fears concerning running such oil blended with fuel, but in a 10% or less mixture.
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:woot
