If you’re looking to determine what your best oil change intervals should be, the best method is via oil analysis. Of course, on small vehicles which require only 4 or 5 quarts of oil, the cost of the oil analysis is nearly as much as a complete oil change.

Of course, the end result is that most folks won’t ante up for a professional oil analysis. However, they might be willing to perform their own “oil analysis”, if they knew how to do it. Of course, such an analysis won’t give you readings as accurate and precise as results from a lab, but it can give you a pretty decent understanding 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 that you can use 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.

- No More Oil Changes – Everything you need to know about oil, but didn’t know to ask

- The Motor Oil Evaluator –

- A Motor Oil Forum for discussion of motor oils

The Business Card Test

Putting this simple test into practice can reveal a plethora of potential oil problems that might necessitate draining of the oil: build-up of condensation, contamination with anti-freeze, high particulate levels, dispersant additive deterioration, fuel in your oil, products of oxidation and sludge build-up.

You should 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 someplace where it will be suspended parallel to the ground 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.

You want to be patient and wait for the paper or card to absorb the oil drop completely which might take awhile. Once all of the oil has been drawn into the pores of the paper you should be able to begin evaluating the condition of your oil.

- A colorless circle or somewhat yellowish outer ring = “good” oil.

- A dense, dark deposit zone = Dispersant additive failure

- A black, pasty area = Anti-freeze in your engine oil

- Center of circle dark with distinct outside ring = Severe oxidation

- A dark center with surrounding rings = Fuel in oil, Fuel dilution

Information for this test featured in: Fitch, J.C., “The Lubrication Field Test and Inspection Guide”, Noria Corporation 2000

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