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It is generally in your best interest to rely on oil analysis to determine your oil change interval. Of course, on many smaller vehicles that need only 4-6 quarts of oil, the price of the oil analysis can be nearly as much as a full oil change.

Of course, the result is that most folks won’t pay for a “true” oil analysis – but they might be inclined to perform their own “oil analysis”, if only they knew how to do it. It won’t give you results 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.

Below you will find one of six very straight-forward yet incredibly useful methods for checking oil quality without ever having to leave your garage.

You might also want to consider learning a bit more about motor oil and filtration in general. The following sites may prove useful for this purpose.

- The Motor Oil Bible – tons of motor oil information

- The Motor Oil Evaluator – motor oil comparison specifications

- A Motor Oil Forum for discussion of motor oils

The Blotter Spot Test

The use of this simple layman’s oil analysis test can expose a wide range of potential oil breakdown symptoms that might lead to the necessity for an oil change: 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.

While your oil is WARM (not HOT), pull your dipstick and put one drop of motor oil on a heavy, white, NON-glossy business card. Place your white paper/card in a location where it sits suspended and horizontal and so that your oil spot will be touching nothing – on the top OR bottom of the card. As an example, if you’re using stiff card stock or a stiff business card (which you really should be) you could set it across the top of a coffee cup.

You want to wait for the paper or card to absorb the oil drop completely which might take awhile. Use the list below to evaluate the condition of your oil based on the DRY oil spot.

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

- A dense, dark deposit zone = Dispersant additive failure

- A black, pasty zone = Glycol (Anti-freeze) in your engine oil

- Center of circle dark with distinct outside ring = Severely oxidized oil

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

Details of the blotter spot test in: Fitch, J.C., “The Lubrication Field Test and Inspection Guide”, Noria Corporation 2000

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