I’ve been asked a couple times now by different persons whether it’s possible to burn used motor oil in a home furnace. The answer is that it is possible, however you wouldn’t want to do it. Take your leftover Mercury engine oil from an outboard motor for example, now you could pour it in your home heating oil tank in place of kerosene, or mixed with kerosene, but this will cause a lot of pollution and an awful smell. Used motor oil contains a lot of dirt and grit particles that when burned up, cause environmental damage and will coat surfaces with a black residue.
There are furnaces designed to be run on used motor oil, but these often contain special filters to remove the dirt and grit, and even then are banned in most states for causing unnecessary pollution.