Been recycling used motor oil. Today I mixed it 50:50 with diesel to make a wood stain for the fence. Look at that color POP. 
Discussion
Aside from color, does this help to preserve the wood in any way?
I'd still be a bit concerned about it washing off, effectively polluting the surrounding soils. Looks like that's not an issue in this cause, but something to keep in mind, if using this near gardens or trees.
Yeah me too, used motor oil is nasty stuff.
It’s just as effective as any oil based stain in terms of waterproofing. Farmers have been using this method for years.
Any oil stain would be a similar issue with surrounding vegetation unless it’s a mineral oil. This particular area I’m not too concerned about toxicity except one spot that grows blackberry. I’ll be observing the area the next year or two to decide if they’re edible or not.
I think most of the toxins off gas pretty rapidly. Kind of like the tires in an earth ship. I’d always thought used motor oil contained dioxin, but this post made me read a little further and it looks like anything that would off gas from using used motor oil as a wood preservative would off gas during the recycling process anyway. I’ve always thought about soaking fence posts in used motor oil.