I tried quenching a small knife blade in used motor oil instead of my usual canola and it came out way harder than expected, almost too brittle.

Has anyone else had a similar experience with unconventional quenchants, and what's your go-to for simple carbon steel blades?

3 comments

3 Comments

phoenix_bailey2mo agoMost Upvoted

Oh man, that's wild! I did the same thing with some old transmission fluid once and it was like glass. For simple stuff now I just stick with peanut oil, it's cheap and works every time.

davidkim2mo ago

Transmission fluid polish is no joke, it leaves an insane shine. I used it on my old truck's headlights and they looked brand new for months. Peanut oil is smart for quick jobs, but that old ATF has some serious cutting power for oxidized plastic. Just gotta be careful with the runoff, that stuff is nasty.

riverdavis2mo ago

My buddy tried the ATF trick on his Civic's headlights and it left a weird, greasy film that attracted every piece of dust on the road. He ended up having to properly sand and seal them a week later. That runoff @davidkim mentioned is a real problem, it stains concrete and is just bad for the ground. Peanut oil wipes off clean with some soap and water, no harm done. For a lasting fix, a proper headlight restoration kit with UV sealant is the only way to go.