Depends on the size, RPMs, running temperature, and application. For small motors up to the size of a small room fan you should use a very light oil. There was a fantastic oil called Corrosion X, but I think it is now made under a different name. Some hardware store teflon sprays are ok but not as good as Corrosion X. 3 in 1 is too thick for small electric motors. Sewing machines have some special oils made for them, those oils are high priced, but are very good.