I tend to use a bit of oil in my shop. I do a bit of suspension tuning and bleeding of hydraulic brakes. As the brakes on my bikes use mineral oil, I end up with a fair amount of high quality waste oil.
As we all know with the “Four R’s” or Waste Hierarchy, reusing suspension and hydraulic oils for chain lube is a perfect use for these oils. I already use the same or similar mineral oils for chain lube so this is extremely similar, just a lighter viscosity in the end due to the suspension fluids.
I decided on an experiment to see how filthy the waste oil actually was.
I first let gravity and the oil separate the heavy macro solids in the oil. There is quite a bit of solids in the suspension waste. After that, I poured off what I could of the clean separation through a coffee filter (approximately 25 µm filtration). The filter was apparently clean after this meaning that very little must have been captured by it. I then filtered the oil through some lab Whatman Filter Paper, Qualitative 24.0cm, Cat. No. 1001 240, #1, 11 µm. Again, no visible sign of contaminate.
This is all quite un-scientific as I’m not really testing the paper to see what it has captured. I’ve just evaluated it visually which can be deceiving. This also assumes that there is no chemical issue with the oil. There may be, but it’s not going to matter in use as a chain lube regardless.
What this does mean to me is that in the future, I will be using this oil for chain lubrication after just skimming off the separation. Very good and nice. I just need to pour it in my customary shop bottles for chain lube.