I always thought quenching in used motor oil was a bad idea until yesterday

I was working on a set of heavy-duty tongs and my usual quench oil was all gone (I use Parks 50). My buddy Mike, who runs a shop over in Redmond, told me to just use the old 10W-30 from my truck, saying it works fine for simple carbon steel tools. I was sure it would leave a terrible finish or not harden right. But I tried it on one jaw, heated to a bright orange, and quenched it for about 8 seconds. The file test showed it was plenty hard, and the part didn't warp or crack. It's definitely not for a fancy blade, but for shop tools it saved me a trip to the store. Has anyone else used old engine oil for quenching in a pinch, and did you notice any downsides?

4 comments

4 Comments

bailey.shane2mo ago

Yeah, I used to think the same thing, that it would be a total mess. But last year I was in a bind with a big punch and used some old 5W-20. It hardened up just fine and the smoke wasn't any worse than my usual fast oil. What kind of steel were your tongs made from?

nancyn692mo agoTop Commenter

Redmond Mike's advice saved my day last spring.

piperbailey2mo ago

Redmond Mike told you to use old 10W-30? Honestly, that sounds like a great way to start a small grease fire in your shop. Tbh, I'd be worried about the smoke and the smell more than the hardness.

the_wesley2mo ago

Ever wonder if the smoke from old motor oil changes based on the base stock? Bailey.shane mentioned using 5W-20, which is usually a lighter group, so maybe that's why it wasn't too bad. I'd be more worried about what additives are left in that 10W-30 after it's been cooked in an engine, that's where the real nasty smells come from. Hardness seems like a gamble when you don't know what's actually in the bottle anymore.