It is generally in your best interest to rely on oil analysis to determine your oil change interval. Of course, on many passenger car vehicles that only take 4-6 quarts of motor oil, the price of the oil analysis is nearly as costly as a complete oil change.

Of course, the result is that most folks won’t pay for a “true” oil analysis – 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 enough information to determine whether you should be changing your oil or not (as long as you don’t push things too far).

As you read this article you’ll find detailed instructions for 1 of 6 DIY oil analysis tests which you can utilize to determine how well your oil is holding up and whether it’s ready for a change. In this way you can begin to set realistic oil change intervals for your vehicle.

It would likely also be in your best interests to learn a bit more regarding lubricants and filters in general. You might find the following sites useful in this quest.

- No More Oil Changes – Over 150 pages of motor oil information

- The Motor Oil Evaluator –

- A Motor Oil Forum for discussion of motor oils

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 of used oil on the surface of chromatography paper (good heavy white card stock works pretty well too) – make sure the engine/oil is WARM (not HOT). Place your white paper/card suspended horizontally above a table or countertop and so that the oil drop area will be touching nothing – on either side of the card. For instance, if you’re using stiff card stock or a stiff business card (which you really should be) you could set the card across the top of a coffee cup.

Be sure the drop dries completely before you attempt to evaluate the appearance of the oil drop. 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 yellowish outer ring = “good” oil.

- A dense, dark deposit zone = Dispersancy failure

- A black, pasty area = 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 the blotter spot test in: Fitch, J.C., “The Lubrication Field Test and Inspection Guide”, Noria Corporation 2000