Why does everyone keep quenching in old motor oil?
I've been noticing a lot of posts on here where folks are using used motor oil to quench their blades and tools. That stuff is full of dirt, metal shavings, and who knows what else from the engine. It makes a huge mess, gives off way worse fumes than fresh oil, and you never really know how it's going to cool your steel. I had a guy bring me a knife he made last month that had a weird soft spot right in the edge, and I'm pretty sure the contaminated quench oil caused it. I've tried a few different oils over the years and I keep going back to canola or a dedicated quenching oil like Parks 50. Is there some trick to using used motor oil that I'm missing, or is it just cheap?