It is best to rely on oil analysis to determine your oil change interval. Of course, on many smaller vehicles that need only 4-6 quarts of motor oil, the price of the oil analysis is nearly as much as a full oil change.nnOf 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 their own “oil analysis”, if they knew how to do it. 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.nnIn 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.nnYou might also want to consider learning a bit more regarding oils and filters in general. The following sites may prove useful for this purpose.nn- No More Oil Changes – Tons of motor oil informationnn- The Motor Oil Evaluator – nn- A Motor Oil Forum for discussion of motor oilsnnPerforming the TestnnUsing just this simple layman’s oil analysis test can shed light on a wide range of possible oil problems which could require an oil change: excessive particulates, condensation build-up, glycol contamination, fuel dilution, failure of dispersant additives, formation of sludge and oxidation products.nnWhile your oil is WARM (not HOT), yank the oil level dipstick and deposit a single drop of motor oil on a heavy, white, NON-glossy card stock or business card. Put your white paper/card someplace where it will be suspended and parallel to the ground and in such a way that the oil drop area won’t touch anything – 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 glass.nnMake sure that the drop is entirely dry before you attempt to consider the condition of the spot. At the point where the paper/card has completely drawn all the oils into itself you can begin evaluating the ability of your oil to continue without a change.nn- A colorless circle or somewhat yellowish outer ring = “good” oil.nn- A dense, dark deposit zone = Dispersant additive failurenn- A black, pasty area = Anti-freeze in your engine oilnn- Center of circle dark with distinct outer ring = Severe oxidationnn- Center of circle dark with outer rings = Fuel in oil,Fuel dilutionnnInformation for the blotter spot test in: Fitch, J.C., “The Lubrication Field Test and Inspection Guide”, Noria Corporation 2000