--The Blotter Spot test
This test reveals oxidation products, sludge formation, dispersancy failure, glycol contamination, water contamination, fuel dilution, and high levels of particles.
You want to place a drop or two of used oil on the surface of chromatography paper (good heavy white card stock works pretty well too). Lay the paper or business card flat, but so that all but the very edges of the paper is suspended. For a fairly stiff business card, placing two pencils down on a table and laying the business card so that the ends are resting on the pencils would work well.
You want to wait for the paper or card to absorb the oil drop(s) which might take awhile. Once all of the oil has been drawn into the pores of the paper you can begin evaluating the condition of your oil.
- A colorless spot or slight yellow outer ring - "good" oil.
- A dense, dark deposit zone – Dispersancy failure
- A black, pasty zone – Glycol (Antifreeze) in your oil
- A dark center with distinct outer ring – Severely oxidized oil
- A dark center with surrounding rings – Fuel in oil
Information for the blotter spot test found in:
Fitch, J.C., “The Lubrication Field Test and Inspection Guide”
Noria Corporation 2000
The Motor Oil Evaluator | Poor Man's Oil Analysis