as long as its oil, it will lube the bar and chain, anything that can help disapate the heat from friction, therefore in a pinch even diesel would lubricate for a time, but the oiler would have to be turned way down to prevent it from just pumping it all out to quickly. And if you use motor oil it should be adusted anyway as well, way to measure is one tank of fuel to about 7/8 tank of oil.... then you are not using any to much .... and ive even turned mine down to half a tank at times.
The problem associated with old motor oil is it splatters everywhere, and if you are cutting logs for log housing, then it stains, luber for siding it stains too......
FWIW
William