There's really two parts to going used oil, either veggie or dino-oil.
The first part is that you need to deal with the oil to filter it and remove any water in it. Then adjust its viscosity so it is not too thick. The filtering thing is real important because some of the orifices in a diesel injection system are so small that bacteria have to go single file through them.
The second part is to set up your truck to handle the oil, especially in cold weather. Thick or gelled oil can seriously ruin your day.
While none of these items is too hard in itself, you need to be willing to set yourself up to do it...it takes some dedication to get to that level. Setting up your truck, setting up your filtering/cleaning/oil storage area, collecting oil, prepping it, getting it into your truck, dealing with the filtered waste, etc, etc.
Having a big monthly fuel bill is a huge incentive!
That being said, it is a bit of a natural fit for anyone that scraps vehicles or industrial stuff. Oil, gas, and other liquids need to be removed from the equipment anyway, so why not re-use it yourself?
There is a decent, simple discussion of using waste oil and some of the details
here. Disclaimer: I don't have anything to do with this guy, except having bought his books and am considering purchasing his centrifuge. He is a Mechanical engineer and explains everything clearly enough that you can check his logic against other information sources. (ie, no "Majic") I might be biased 'cause I'm a Mechanical engineer, too.
Hope this helps,
Jon.
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