Excellent points here. One of the things about Biodiesel is that it will clean the crud out of anything you put it in. Ie, put it in an old tank and anything built up over the years will loosen and go where the fuel goes. A good filter will soon plug up and you get little or no fuel to the engine. You will then have to change filters often until the crud is removed. A place where I used to work had an overhead gravity tank with no filter which they had used for years to store the diesel fuel for their JD lawn tractor. Never had any problems until they decided to go to biodiesel--big mistake. Less than the first tank of biodiesel and the tractor started running bad. Long story short, they didn't keep changing the filters and destroyed the engine. With diesel (or biodiesel), you need to obtain clean fuel, keep it clean, and filter it every time you move it from one container to another.
Having said all that, the blend with used oil will work, but filter, filter, filter, and a coffee filter will only get the larger contaminates out. It's those particles which are too small to see which will cause the problems. Actually, the engine will run on just the oil.
Got a buddy who runs veggy oil, and or used oil, mixed with diesel in his truck. He has a filtration system to ensure it's clean before it goes into his truck though.
I'm with rustyshakelford, diesel fuel, or even biodiesel, from the station is cheap. The limited amount of fuel my x900 will burn in a year is not worth any potential fuel cost savings recognized from blending my own fuel or using alternatives. Now in my larger, older diesel tractor, I could consider a used oil blend. Probably will not do that either though.
