The best way to establish realistic oil change intervals is via oil analysis. Of course, on many passenger car vehicles that only take 4-6 quarts of motor oil, the cost of the oil analysis is nearly as much as a complete oil change.
Of course, the result is that the vast majority of vehicle owners choose not to pay for professional oil analysis services – but they might be willing to perform a simple oil analysis themselves, if they knew how it could be done. It won’t give you readings as accurate and precise as results from a lab, but it can give you a fairly good idea of how well your oil is holding up.
In the next few paragraphs you’ll find detailed instructions for one of six DIY oil analysis tests which can be used to establish the condition of your oil and whether it’s ready for a change.
You might also want to consider learning a bit more regarding oils and filters in general. You might find the following sites useful in this quest.
The Spot Test
This test reveals oxidation products, sludge formation, dispersancy failure, glycol contamination, water contamination, fuel dilution, and high levels of particles.
While your engine (and the oil) is WARM (not HOT), yank the oil level dipstick and put one drop of engine oil on a heavy, white, NON-glossy card stock or business card. Put your white paper/card in a location so that it sits suspended and horizontal and so that the oil drop area will be touching nothing – on the top OR bottom of the card. For instance, if using something relatively stiff you could place it across the top of a coffee cup.
You want to be certain that the oil spot dries completely before you attempt to evaluate the appearance of the oil drop. At the point where the paper/card has completely drawn all the oils into itself it is then time to begin evaluating the ability of your oil to continue without a change.
– A colorless circle or slight yellowish outer ring = “good” oil.
– A dense, dark deposit zone = Dispersancy failure
– A black, pasty zone = Glycol (Anti-freeze) in your engine oil
– Center of circle dark with distinct outside ring = Severely oxidized oil
– Center of circle dark with outer rings = Fuel in oil,Fuel dilution
Information for this business card test in: Fitch, J.C., “The Lubrication Field Test and Inspection Guide”, Noria Corporation 2000