Engine Oil Analysis Best Practices

Bennett Fitch, Noria Corporation

Engine Oil Analysis Best Practices


The benefits of oil analysis are enjoyed throughout all industries that operate mechanical equipment. But what about the common machine most of us take for granted for its ability to get us from point “A” to “B” without fail?

Yes, I’m talking about our personal passenger vehicles.

Most of us would be frustrated and inconvenienced if our car suddenly ceased to provide its basic function. You likely have experienced this problem in the past for at least a day or so. As with most any other machine, our vehicles require routine maintenance.

Whether you perform the maintenance on your car or rely on a mechanic, there are several inspection points and areas of concentration throughout the vehicle. Historically, tire-related failures are the primary cause of breakdown.

With most tire issues, the cost of repair and the length of downtime are low, especially if the remediation is simply a repaired flat. On the other hand, engine failure is far less common but can be very expensive and often results in downtime of several days or weeks, depending on the availability of spare parts.

Why Passenger Vehicle Engine Oil Analysis Is Rare

There are many reasons oil analysis is not commonly performed on passenger vehicles. Car owners usually are not interested in extending their engine’s life because they don’t anticipate a significant failure during their ownership period. Most don’t hold onto a new vehicle for more than five to 10 years. The majority of car owners also expect their insurance or warranty policy to cover any potential engine failure.

In addition, many people believe that simply changing the oil and oil filter routinely is sufficient to maintain their car’s engine. They don’t consider that the cost of engine oil analysis testing may be similar to that of an oil change. Some vehicles also have an onboard “oil life” indicator that provides real-time feedback to the driver about the engine oil’s condition, which may give a false sense of security. 

Even if you understand the benefits of engine oil analysis, collecting a sample on a passenger vehicle is inconvenient and ineffective. There generally is no good location to take a representative oil sample. Without an engine retrofit, the sample normally will be taken from the dipstick port via the drop-tube method or from the drain port during an oil change.

These are only a few of the reasons why there isn’t much of a market for fluid analysis of passenger vehicles. However, one of the most important aspects of oil analysis is often overlooked, which is the ability to provide information about the contamination and wear debris in the oil.

Why Passenger Vehicle Oil Analysis Should Be Performed

Oil analysis not only is effective in offering indicators of oil condition, but it can also identify various forms of contamination and wear debris as an engine condition monitoring indicator. This should be of even greater importance, since the longevity of the engine and the vehicle is the goal of any analysis performed, not just the quality and longevity of the oil.

The bulk of oil analysis performed in North America is on diesel engine oil. This is because the vast majority of these diesel engines are powering heavy-duty trucks for large transportation fleets or industries with off-road equipment.

These fleet owners and owner-operators are reliant on the continuous operation of their trucks to produce revenue and income. This dependence can be risky, and thus oil analysis provides them with an added level of assurance toward improved reliability.

Engine oil analysis can be just as beneficial to most owners and drivers of passenger vehicles if the right information is obtained. Among the key questions to ask about the oil in your car include:

  • Is the right engine oil being used?

  • Are certain additives or base oil properties depleting or degrading too rapidly? 

  • Are there external contaminants in my oil that shouldn’t be there? 

  • Are there internal contaminants like fuel, soot, coolant, etc.?

  • Is there an indication that the engine is generating abnormal amounts of wear? 

  • Is the type of wear indicative of an incipient failure?

  • Is the cause of the generated wear unique to a known type of failure? 

Where and How Often to Perform Oil Analysis

With most oil analysis of industrial plant equipment, a sample is collected every “X” number of weeks or months and evaluated using a predetermined set of routine tests.

This is practical when the cost of oil extraction and replenishment is reason enough to extend the drain interval until it has reached its condemning limit and when pulling a sample during operation is effortless because of an installed sample port. Even if it isn’t costly to replenish the oil, it may be important to monitor machine conditions through engine oil analysis simply because the machine is critical.

The typical passenger vehicle is not equipped for proper oil sampling during operation. The ideal sampling location would be on the pressure line between the pump and filter on a wet-sump system.

Since this is not feasible, it generally is better to opt for sampling at the drain port during a drain-and-fill or via the drop-tube vacuum sampling method. Keep in mind that there are best-practice procedures for these two sampling locations that should be considered before continuing with these approaches.

Sampling frequency is primarily based on the potential for oil analysis to offer an early indication of an unusual contamination issue, rapidly degrading oil or impending machine failure condition. Oil analysis is unique in that it can detect a possible concern long before other sensors or external symptoms are often triggered.

Since oil drains normally are more frequent in passenger vehicles than other machinery, the best sampling interval for the engine most likely would be right before the scheduled drain interval. As long as the sampling interval time is normalized relative to the previous oil change, the individual interpreting the data has an opportunity to effectively trend the data points.

This strategy is beneficial because it not only will yield a variety of information about the engine’s health but also help determine if the current drain interval is too long or short.

Which Oil Tests to Use

Engine oils can be analyzed to obtain valuable information about their properties, contaminants or wear debris. The instruments in an oil analysis laboratory may focus on one specific piece of information or be designed to report multiple points of information. The following are some of the most common engine oil tests.


This test measures a fluid’s resistance to flow and shear. Viscosity is an oil’s most important property. It provides the basic function for creating a film thickness between mechanical surfaces moving relative to one another. The engine oil in your vehicle is formulated to match a particular viscosity.

If the viscosity changes, the oil may not be sufficient to protect the engine’s surfaces. It can also mean that the oil has chemically degraded or been affected by a contaminant such as water, fuel or glycol. When this occurs, it will be necessary to further investigate the potential root causes with other oil analysis tests. 

Base Number

Base number testing is used to measure the reserve alkalinity within the oil. This characteristic of engine oils is intended to neutralize the acidic compounds to which the oil may be exposed through blow-by contaminants. The base number will trend downward as the oil ages, but a rapid change could be an indicator of increased blow-by contaminants due to inefficiencies in the combustion zone, severe running conditions or using the wrong oil.

Particle Count

A particle count test identifies the level of general contamination in the form of three numbers representing the amount of contaminants greater than 4, 6 and 14 microns per milliliter of fluid. Contamination exposure to the engine oil can be detrimental, but it is expected during operation of the vehicle.

Particle counting results can tell you several things, such as the potential ineffectiveness of the intake air filter or the oil filter. For example, if the oil filter has ruptured, it may not be removing contaminants sufficiently, allowing them to become continually ingressed into the engine oil.


Water content is generally determined using the Karl Fischer test, which reports the amount of water present in oil in parts per million. An oil sample may also be screened first through a crackle test. Water in oil is particularly concerning because it can lead to rapid oil degradation and a corrosive reaction to iron and steel mechanical surfaces.

The source of water must be investigated if abnormal amounts are found. These sources could include leaks from the oil cooler, high levels of moisture in the environment or inefficient running conditions.

75% of lubrication professionals do not perform oil analysis on their car’s engine oil, based on a recent survey at MachineryLubrication.com

Ferrous Density

This test focuses on increased levels of ferrous wear particles present in the oil sample. Once wear debris is observed at abnormal levels, remediation actions must be taken seriously, as the potential for engine failure is impending. Unlike solid contaminants and moisture, which are root causes that could lead to failure, increased levels of wear debris indicate that mechanical wear is already occurring in the engine.

This may be a consequence of inaction to the contamination levels or poor lubrication due to changes in oil properties. It could also be a result of changes in operating conditions or mechanical inefficiencies.

Analytical Ferrography

If wear debris has been observed at abnormal levels, additional techniques can be used to examine it more closely to obtain clues as to its severity and root cause. This microscopic review of wear debris particles includes characterizing the general shape, size, color, reflectivity, edge details, markings and concentrations.

The results can help establish from which components the wear particle originated and by which wear mode the particle was produced. These details can be useful in understanding how severe the problem is and if remediation actions are required.

The patch test is a similar method used to observe insoluble deposits on a porous membrane through which oil has been pulled. It offers a means of analyzing concentrated amounts of contaminants or oil degradation byproducts.

Fourier Transform Infrared (FTIR) Spectroscopy

FTIR provides information about not only the oil’s health but also contaminants like soot, water, glycol and fuel, as well as oil degradation byproducts such as oxides, nitrates and sulfates. It employs a unique technology that observes constituents within the sample at the molecular level. While the test excels in its capability to review a broad spectrum for analysis, its accuracy can be somewhat limited.

Elemental Spectroscopy

Elemental spectroscopy is similar to FTIR, but instead of observing constituents at the molecular level, it is able to report details about the oil at the elemental level. The results are most valuable after they have been trended with a reference sample or a history of samples from the same engine.

As elemental concentrations increase or decrease, the trends can be correlated to specific wear patterns, contamination level increases or a depletion in additives formulated within the oil.

Other possible tests include flash point, fuel dilution, acid number, optical soot meters and blotter spot testing. The exact combination of tests to perform will depend on the types of questions you need answered.

Whether you are a hot-rod owner who can’t bear the thought of an engine failure or a casual vehicle owner who doesn’t want to be inconvenienced by a breakdown, there are good reasons to perform engine oil analysis. The oil in your engine is full of details, and it’s just waiting to give you an update on how the engine is doing. So the next time you change your oil, consider taking a sample and having it tested.


Fitch, J.C. (2012). Analysis of In-Service Automotive Engine Oils. S.C. Tung & G.E. Totten (Eds.), Automotive Lubricants and Testing

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About the Author

Bennett Fitch is the Chief Strategy Officer (CSO) for Noria Corporation. His years of experience at Noria includes director of development for Lubrication Program Development (LPD) services and ...