We make a few hundred gallons of flush oil a month at work. Everytime a different product is pumped through a line, about 5 gallons is written off for flush.
Like I fill a 15w40 tank and next is a 0w30 tank, line is flushed. Or in some trucks only have 1 pump so might be pumping ATF, then engine oil, hydraulic oil, etc.
Anyhow, it provides me with heat. I've never considered using it in anything.
When I helped out at a small engine shop I fixed DOZENS of oiling systems on saws that people decided running used engine oil for bar lube made sense.
Not only would it plug everything in the oil system or kill the pump, but fling everywhere and plug the cooling fins, and eventually seize the engine.
Maybe if it was filtered and some sort of tackifier added it'd be ok. But the proper oil is $10 a gallon and most don't use but a gallon or 2 a year anyhow.
I've been using really old SA rated 30wt, 40wt, first edition SL rated 10w-30, first edition SM rated 30wt and really old ATF mixed with any of those oils during the winter for years now. Most recently I've added 2.5 gallons of ancient SH rated 30wt oil to bar oil stash.
For right now my saw bar oil and break in oil is just really old but still virgin motor oil. At the moment I have plenty of it and I'll probably use it all in saws mostly and new engines and it will be gone by early next year unless I discover more.
It flings everywhere because the pump is actually able to pump enough of it and keep the bar cool.
Project farm did a test of saw oils. The motor oils and repacked motor oil as saw oil did the best.
When used oil clogged everything up I bet they used oil that ran down the dirty oil filter and ran down the dirty oil pan and into an even more dirty catch pan that had nasty oil from lawnmowers, differentials and whatever dumped out of oil filters in there too. Probably didn't even try to filter it then wonder why it clogged up their saw.
My reclaimed motor oil starts off by cleaning around the drain plug. I pull the drain plug let the first half quart or so of oil fall into the dirty oil catch pan, then catch the oil I want to save in an oil jug that only ever had new oil in it prior to that moment.
But what about the oil that comes off the oil filter? Straight into the dirty catch pan with the combustion grade oil, don't even try to save what runs down the filter or what was in the filter.
Since stuff settles out of my cleanest reclaimed oil I dump the last half quart into my combustion grade oil jug, or that reclaimed jug gets marked to be combustion grade.