I bought a Gravely tractor back in 2016,, this is it, before I unloaded it from the trailer,,
The FIRST thing I did was drain the oil, both engine, and transmission,, it had been setting a LONG time.
Well, the oil that came out looked like the oil out of a Mobil 1 jug that had just been purchased at Walmart!!
After a little tinkering, I got it started, and the new oil I installed was dirty in about 5 minutes.
All the dirt
(I mean ALL!!) had settled out of the oil. Sure, the acids etc did not settle out,, but, that old oil was clean.
That oil would have been perfect for chain oil.
Now I have several jugs of drained oil setting in a shed, as an experiment,, to see how long of setting is required to clean that oil.
I saw this big contraption at an antique store in Pennsylvania. after looking at it a while, I figured out what it was.
Back in the 1930's, the engine oil was non-detergent,, the dirt would settle out of the oil FAST..
The contraption was about as big as a 275 gallon heating oil tank.
The farmer would drain the oil out of his equipment, then place it in this tank,, there were a number of compartments.
After putting the drained oil in one compartment, he would use the oil that had been setting the longest, and refill the engine.
The tractors did not even have air filters, in many cases,, the engine oil ended up capturing the dirt.
There was ALWAYS LOTS of dirt to settle out.
Now, with detergent oil, the dirt will stay in suspension much longer,,
BUT, given time,, most of the dirt will settle back out,, and the oil will be clean enough for bar/chain lube.
I almost hate to mention the other method of cleaning oil. I might get shot,,,,,,,,,,,,,,,,,,,
Anyways,,
back in 1966, there was a gas station near my home in Pittsburgh,
The guy had a contraption in the back room,,
He would drop 6 or 8 rolls of toilet paper in a long tube.
Then, used oil was added to a tank at the top. Then over a LONG time, the oil would filter through the TP,,
Clean looking oil came out the bottom,, He would "sell" the cleaned oil as "bulk oil" which was dispensed with a clear glass funnel top bottle.
I think he made a lot of profit off of the used oil.
Many cars burned/leaked lots of oil,, Why spend a lot of $$$ on oil that will be out of the engine in 200 or so miles?
If you "waste" TP cleaning oil,, don't tell them it was my idea,,,
it is hard enough gettin' TP to use as TP!! LOL!!
So, maybe used oil does not have to be horrible (well, except diesel oil, I doubt that anything will help that engine oil)