When I was setting up my oil-soaked rag in a can, I didn’t have mineral oil at hand. So I decided to use what I had until I could get a supply of mineral oil. The oil I had available was 30w motor oil. It does leave a small stain on the wood for the first few swipes with the plane or saw, but this is removed with subsequent passes. I’ve been using this motor oil for about 6 months on plane soles, saw plates, and chisels, and have found no reason to bother switching to the lighter mineral oil.