It is a common misconception that an oil's color is an indication of how "dirty" it is. This is not true. It is often a common tactic used at quick lubes and service centers; the technician pulls the dipstick and wipes it on a white shop cloth and shows the customer how "black and dirty" it is. Any oil will turn black after a short period of use. Some oils may stay "clean" looking longer than others, but eventually they all will turn black. This is perfectly normal.
When someone tells me how "clean" their oil is because they have pulled the dipstick and it looks clean I always tell them that it will eventually turn black. They also tell me when they pull the dipstick and it has becomes black and "dirty" it will require changing. That's about the time I will pull my dipstick in one of my trucks and show them how black and "dirty" the oil is. I will then produce my latest oil analysis test report that provides laboratory chemical and spectrographic test data confirming that the oil perfectly suitable for continued service.
In general, the color of an oil does not have any bearing on its lubrication ability or whether or not the oil is suitable for continued use*. Most oil and especially diesel engine oil will turn black in the first few hours of operation due to contaminates generated by the combustion process and soot particles. It is the job of the filtration system to filter out the larger sized soot particles that can cause engine wear and the additive package of the oil to neutralize and hold in suspension the soot particles that are too small for the filter to trap and hold.
* Under certain conditions such fuel dilution, water contamination or glycol contamination, for example, the color can provide insight that something is mechanically wrong and in need of repair and/or additional analysis, however under normal operating conditions without mechanical problems present the black color which is commonly referred to as "dirty oil" in the vehicle servicing industry does not have any bearing on its lubrication ability.
The only way to accurately determine an oils lubricating value or contamination level is through (spectrographic) oil analysis. Oil analysis is common practice used regularly in commercial, industrial and fleet operations and can also be used for passenger cars, light trucks or any other application.
The useful life of an engine oil is dependent on several factors such as the quality of the oil, additive package blended in the oil and the TBN level of the oil (the ability of an oil to neutralize acidic by-products of combustion), type of fuel, equipment condition, type and operating environment of the equipment and the type of filtration.
The filtration system and the oil are vital tools for preserving engine life. A highly efficient oil filter is essential to protect an engine by removing both liquid abrasive contaminants held in suspension by the oil. It must be stated and understood with critical importance that there are wide variances in the quality of motor oils. Certain lower quality oils do not have quality base stock oils and additive packages to support long drain intervals while other higher quality oils can have significantly longer drain intervals. AMSOIL is engineered, specified and guaranteed for either 25, 000 miles/1-year or 35,000 miles/1-year, depending on the products used, in non commercial gas engine passenger cars or light trucks, without the need to perform oil analysis.
Also keep in mind that the micron rating of an engine oil filter means absolutely nothing unless the efficiency (particle capture percentage) of the filter is stated also. If a filter is stated to be a "10 micron filter" but the efficiency graph shows it only traps 5% of the 10 micron particles then it isn't doing much good at filtering out 10 micron particles.
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