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"Waste" motor oil has a lot of uses. It's still a good lubricant for many purposes, just not for high-temp high-speed internal engine parts. It's also very similar to heavy diesel fuel, and could be burned in an oil furnace or heater, or smudge pots. Same thing with used auto transmission fluid. It can also be used as a quench if you're doing any metalwork that requires forging & hardening.