canola or peanut oil heated up to 130-140 degrees before you quench works a lot better than cold oil or used motor oil.
those 2 vegetable oils also have a pretty high flash point and the smoke from them isn't as toxic as petroleum based oils.
If, OTOH, you have access to an actual engineered quenching oil, that will work even better -- but you still want to heat it.
heat our file up until it is glowing red and a magnet doesn't stick, then quench.
keep it moving in the oil - but only up/down or front to back - side to side like a paddle can cause it to cool at uneven rates and warp.