The Meaning Of Engine Oil Color

by Ryan 426

It is a common misconception that an oil's color is an indication of how "dirty" it is. This is not necessarily accurate. 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 will all 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 out and it has become 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 is 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 in all internal combustion engines (and especially diesel engine oil) will turn black often 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 oil's lubricating value or contamination level is through (spectrographic) oil analysis. Oil analysis is common practice and is used regularly in commercial, industrial and fleet operations and can also be used for, motorcycles, ATV's, powersports equipment, passenger cars, light trucks or any other application. It is an especially useful feedback tool for technicians, drivers and engineers in all types of racing and high performance motor sport applications

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 oil and air filtration.

If the oil manufacturer's product you are using does not have a change interval specified on the bottle, or product data specs sheet, then either change it at the equipment manufacturer's intervals or perform oil analysis testing to determine the condition of the engine oil at the time you think it should be changed.

This can be a very useful tool, not just for the oil but also for the condition of your engine. Once you perform a few tests you will be able to establish a trend for your type of vehicle's oil and use, and can then determine a practical oil change interval for future changes without the need to perform oil analysis testing each time.

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 intense heat, shear forces, and longer drain intervals, while other higher quality oils can have significantly longer drain intervals.

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. For example, one particular oil filter manufacturer's oil filters are 98.7% efficient absolute at removing 15 micron particles. Note that this is an absolute number and not a nominal rating as many other filters are rated at.

- Phew. That's a lot to filter through (sorry I couldn't resist the pun).. Fantastic information Ryan. Do you work for an oil company or are you just a smart cookie who owns a fleet of trucks?

Hayden -

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Jan 14, 2013
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Oil Analysis
by: Anonymous

The best way to assess the quality of oil is to send off a sample for analysis (I use roktex.com) where they can send you information on contaminants, wear metal levels and the remaining additives in your oil.

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