hi just a quick question, i have a large leaf spring knife to quench so i would like to add to my quench oil (it has seen only two small knives) do i have to add the same type of oil ie, 10 w 40 or can i mix in ie, 5 w 30 or even canola oil ??? i have some of each.please help as im now stuck.thank you

go with the straight canola

When you stray the path and start experimenting it may give you false results. If it works you will not for sure know why if it fails you again will not know for sure why. The best way is to choose one quenchant that applies to the steel you are useing and stick with it for a few years. Keep notes of success and failures. eliminate guesswork. If x oil always has worked with a certain steel that is wot to use. Then if you change or mix and it fails you can record those results and go back to x.
If you are new to heat treat and this mix fails how will you knoif it is temperature, time, oil, or bad steel. If non of what I said makes any sense at all mix away and I hope it works out great.

thanks for sayin what i knew to be true ,i just thought id ask in case i was assuming wrong, im just cheap so i was using donated oil , i will spring for canola.

i did some looking about this topic today.... everything i have found said to use one type of oil dont mix