Determining Proper Oil and Filter Change Intervals: Can Onboard Automotive Sensors Help?

Jim Fitch, Noria Corporation

In recent years, the cost of inappropriate drain intervals to the economy, to the environment and to car owners has received closer inspection. In the United States, the average car owner changes his/her oil at just less than 5,000 miles. Conversely, in Europe the average oil change interval is more than 10,000 miles.

Assuming 10,000 miles is a more optimum interval, approximately 300 million to 400 million gallons of engine oil (worth about $1.5 billion, not including labor) in the United States are consumed unnecessarily. With increasing environmental and economic pressures, the potential waste can no longer be easily glossed over.

There are, however, negative consequences to overextended oil drains. In diesel engines for instance, overextended oil drain intervals have been shown to increase engine wear by more than 20 percent with a corresponding reduction in horsepower and fuel consumption. One could safely project that overextended drains in passenger car applications would have a similar negative outcome. This of course presents a real dilemma to the car owner.

What exactly is the correct interval? In the quest for optimum lubrication, car owners often receive conflicting advice from vehicle owner’s manuals, mechanics, quick-lube operators and auto parts merchants. Some of this advice is peppered with strong admonishments for bucking conventional wisdom.

As a practical matter, we must consider a range for an oil change from around 2,000 miles to well over 15,000 miles. Most car makers generally recommend changing the oil for automobiles and light trucks burning gasoline once a year or every 7,500 miles, whichever occurs first. For diesel engines and turbocharged gasoline engines, the recommendation is typically a more accelerated 3,000 miles or six months.

Diesels tend to generate much more soot and acidic combustion blow-by in the crankcase. Turbochargers subject motor oils to high temperatures and are more prone to form engine deposits. A turbo can spin at speeds exceeding 100,000 rpm (about the same speed as a dentist’s drill).

When an engine is shut off, the heat inside the turbo bearing housing builds from the high frictional heat and hot exhaust gases. The oil in contact with these hot bearing surfaces can crack, forming coke (hard carbon deposits) and hydrogen. This can lead to bearing damage.

If you read the fine print in your car owner’s manual, you will see that the 7,500-mile change interval is for vehicles driven under normal or ideal conditions. This is where the problem lies. What exactly are these ideal conditions and what are the consequences of not ideal with respect to motor oil condition and engine wear?

What many perceive to be “normal” driving is actually “severe service” driving from the standpoint of the oil. For instance, the following are examples of severe service driving: frequent short trips (especially during cold weather), stop-and-go driving, driving in dusty conditions (gravel roads, etc.), and high-temperature conditions. Under such conditions, the general recommendation found in owner’s manuals is to change the oil every 3,000 miles or six months.

The real problem rests in the attempt to generalize. In reality, there are many unique conditions and factors that influence the decision. For illustration purposes, these conditions and influencing facts can be categorized in two ways as shown in the lists below:

1. Factors and Conditions That “Shorten” the Oil Change Interval:

  • Short-trip Driving - The problem is most pronounced for frequent trips under five miles in cold wintertime conditions. Water and fuel have a tendency to accumulate in the crankcase when the oil temperature doesn’t reach the thermostat setting.

  • Road Dust - Driving in dusty conditions (dirt/gravel roads) with an economy-grade oil filter can turn your motor oil into more of a honing compound than a lubricating medium. The dirty oil generates more wear metals which increase the risk of sludge formation and corrosion from acids.

  • High-Mileage Engine - Engines with more than 75,000 miles generate more blow-by gases, unburnt fuel and corrosive agents that enter the crankcase oil. 

  • Diesel Engines - Diesels produce more soot and acidic blow-by products.

  • Flex Fuels - Alcohol-gasoline blends are prone to accumulate water in the crankcase.

  • Turbo-charged Engines - High temperatures distress the base oil and additives.

  • High Oil Consumption - While on one hand high oil consumption replenishes additives, on the other hand the affliction is also associated with high blow-by of combustion gases into the crankcase.

  • Hot Running Conditions - Hot running conditions, including desert terrain, in general can lead to premature oil oxidation, volatility problems and rapid additive depletion.

  • Desire for Long Engine Life - Shorter drain intervals increases the safety margin in the event of premature oil failure.

  • Towing/Heavy Loads - Generally relates to hot running conditions, thin oil films, higher shearing of viscosity index improvers and more wear metals in the oil. Wear metals catalytically shorten oil life, causing premature oxidation, sludge, acids and deposits.

2. Factors and Conditions That “Lengthen” the Oil Drain Interval:

  • Synthetic Lubricants - Premium synthetic lubricants have excellent oxidation stability, thermal stability and shear stability.

  • High-Capture Efficiency Oil Filter - Controls catalytic wear metal production.

  • Highway Miles (predominate) - Lower average engine revolutions and fewer operating hours per distance traveled (miles) compared to slow-speed urban driving.

  • New Engines - Low levels of engine blow-by after the first 500 to 5,000 miles and less than 50,000 miles (unless oil consumption is high).

  • Frequent Oil Inspections - Simple and frequent oil inspections can be effective at identifying various motor oil problems. Refer to the article titled “Dipstick Oil Analysis” in the November-December 2003 issue of Practicing Oil Analysis magazine.

  • Environmental Concerns (waste oil) - Emphasis on reducing waste oil generation.

  • Low-value Vehicle - Many owners of automobiles with low resale value prefer extended drains to keep their costs low. Others use frequent oil changes as a strategy to limp along a car in its twilight years.

For most of us, distilling all this down to an optimum oil change interval is like trying to nail Jell-O to the wall - too many variables and too much guesswork. There has long been a need for a practical and effective workaround. Rather than attempting to quantify the collective impact of these many conditions and factors, the best approach might simply be for the oil to tell us when it needs to be changed. Oil analysis - now there’s a fresh idea!

More and more oil analysis laboratories are targeting passenger car owners to grow their market. However, as a practical matter, laboratory oil analysis is out of reach for nearly all except for hardcore car enthusiasts. This has led to a flurry of new onboard sensors and related technology being advanced by companies with sizeable research budgets, eyeing the huge transportation industry. The following is a review of these many new and evolving innovations.

Current and Pending Technologies

General Motors Corporation GM Oil-Life™ System

The General Motors (GM) Oil-Life System, first introduced commercially in the 1998 Oldsmobiles, determines when to change the oil and filter based on several operating conditions. The technology does not actually monitor any single quality or physical property of the oil. Instead, the Oil-Life System monitors engine revolutions, operating temperature, and other factors that affect the length of oil change intervals.

The sensor is based on GM’s determination that nearly all driving conditions can be grouped into one of four categories: easy freeway driving; high-temperature, high-load service; city driving; or extreme short-term, cold-start driving. GM discovered that oil degradation in the first three categories was largely a function of the oil temperature. During extreme short-trip driving (the fourth category), the principle cause of oil degradation is water condensation and contaminants in the oil - the lower the oil temperature, the greater the contamination.

The software automatically adjusts the oil change interval based on engine characteristics, driving habits and climate. When the system notifies the owner that it is time for an oil change, the owner can go to the nearest GM dealer and a technician will change the oil and filter, properly recycle the oil, then reset the vehicle’s oil life system.

If the owner prefers to change his/her oil, the GM owner’s manual provides instructions on resetting the timer. Because the Oil-Life System does not actually sense oil condition, it is important for the engine computer to know when an oil change takes place. Therefore, the Oil Life System must be reset each time to ensure accurate and proper performance.

It is now available on all light-duty North American GM cars except for some models of Buick Park Avenue and Le Sabre, Pontiac Bonneville and Sunfire/Sunbird, Chevrolet Tracker, Cavalier and Malibu, S10/Sonoma trucks, Astro/Safari Vans, and the Pontiac Vibe.

DaimlerChrysler Corporation Flexible Service System

DaimlerChrysler’s version of the oil monitor is called ASSYST in Europe and the Flexible Service System (FSS) in the United States. Like GM’s sensor, the FFS uses a computerized system to track multiple engine operating conditions. From research on oil quality through the span of an engine’s life, Daimler discovered that the breakdown in oil is determined by such factors as driving habits (frequent short trips vs. long trips), driving speed and failure to replenish low oil levels. Therefore, the FSS monitors time between oil changes, vehicle speed, coolant temperature, load signal, engine rpm, engine oil temperature and engine oil level. It uses this information to determine the remaining time and mileage before the next oil change and it displays the information in the vehicle’s instrument cluster.

In addition, Daimler discovered that oil degradation is correlated directly with its ability to conduct electric current. Therefore, Daimler has fitted V-6 and V-8 engines with a digital oil quality dielectric sensor, that is mounted above the oil pan along with an analog oil level sensor. This sensor measures changes in capacitance, which effectively is a proxy for the amount and type of contaminants and oil degradation products present in the oil. An increase in dielectric constant (less resistance to electrical flow) indicates oil contamination and degradation.

Daimler-Benz (Mercedes-Benz) has been incorporating the sensor into its vehicles since 1998.

Delphi Corporation INTELLEK® Oil Condition Sensor

The INTELLEK Oil Condition Sensor uses both a computer algorithm as well as a sensing element that directly measures various oil properties. The algorithm takes into account important factors affecting the rate of oil deterioration like temperature, driving severity, oil level and oil type. It measures the temperature every 10 seconds to verify whether it reaches a specific normal operating temperature before the engine shuts off. It also records the number of times the engine turns on and off.

A proprietary capacitive sensing element is the core technology. It tracks the oil’s conductivity, detects water and glycol contamination, oil temperature, and determines the oil level. According to Delphi, the oil’s conductivity is important because it characterizes additive depletion and changes in viscosity and acid number.

The INTELLEK Oil Condition Sensor tracks the many different parameters using onboard software to indicate when the oil is nearing the end of its service life. It attaches to the oil pan or wherever there is a continuous flow of oil.

Continental Temic Microelectronic GmbH QLT Oil Condition Sensor

The QLT sensor was launched in 1996 to monitor engine oil quality, level and temperature. Two sensors simultaneously and continuously monitor diesel engine oils containing soot. The instrument also monitors nitric oxide and oxidation products in spark-ignited engines, as well as water and fuel contamination. Because these factors influence the oil’s electrical properties and permittivity (ability of a material to resist the formation of an electric field within it), an effective oil condition sensor is achieved, according to the manufacturer.

The QLT also has an integrated precision probe that allows it to measure critical temperatures and exact oil levels. It can track temperatures ranging from -40°C to 160°C. The oil level, up to 100 milliliters, is calculated by a second capacitor.

Voelker Sensors Inc. Oil Insyte

The Oil Insyte sensor uses a patented technology based on the electrical properties of an oil-insoluble polymeric bead matrix (see Automotive Sensor Technologies Explained below for more details). The Oil Insyte employs an in-line method for continuous oil condition monitoring with an LCD readout providing detailed information about oxidation, additive depletion, soot contamination and oil temperature. The technology does not require external calibration standards and reports oil condition independent of viscosity.

Voelker Sensors Inc. - Oil Insyte

According to the manufacturer, the sensor measures key indicators of oil degradation and allows the conventional analyses approach of oil monitoring (sampling and analysis) to be combined into a single more efficient analysis. No assumptions are required as to the condition of the engine or the initial baseline quality of the oil.

The Oil Insyte technology measures oxidation and additive depletion, and has the ability to examine the interdependence between the two. They claim difficulties encountered with sensors that measure only the electrical properties of oil (conductive additives masking the true condition of the oil) are overcome by using a differential technique where the conductivity of the bead matrix is measured relative to the conductivity of the oil. The true polar condition of the oil can then be determined.

The soot detection feature of the sensor determines the amount of undispersed agglomerated soot (vs. dispersed finely divided soot) present in the oil. Depending on the oil’s additive package, the same amount of undispersed soot can be present at 1 percent to 2 percent (for the base oil without dispersants) as a fully formulated motor oil with more than 7 percent soot.

Lubrigard Ltd. Lubrigard Oil Condition Monitoring Sensor

Lubrigard Ltd. - Lubrigard Oil Condition Monitoring Sensor

The Lubrigard sensor unit is designed to be fitted by the original equipment manufacturers (OEMs) to new cars and trucks to warn the operator of abnormal lubricant conditions. According to the manufacturer, it indicates when an oil or filter change is necessary or when the oil should be inspected or tested.

The sensor was designed to optimize oil drain intervals and to detect problems like coolant leaks, metallic wear debris and oil degradation by direct measurement. It is particularly useful for measuring high concentrations of soot in diesel engines’ crankcase oils.

The sensor’s technology is based on the dielectric loss factor, also known as Tan Delta. According to Lubrigard, this method is more sensitive to changes in contamination than other dielectric measurements. At the same time, it is tolerant of normal differences in operating temperatures and lubricant formulations. To compensate temperature variations, a temperature sensor communicates with the unit’s microcontroller. The technology monitors soot, water, coolant, oxidation and/or wear particles.

The sensor is designed so that it can be connected to the car’s onboard computer. Outputs and alarms are displayed in accordance with the auto maker’s preference. For example, a dashboard display could show a thermometer-type scale growing in size and changing color from green through amber to red as the oil degrades.

The Lubrigard sensor is readily mountable on any engine, gearbox or hydraulic system, and it will work in both gasoline and diesel engine oils.

Symyx Technologies Inc. Solid-State Oil Condition Sensor

Symyx Technologies developed a sensor that uses a solid-state micromechanical resonator and a special signal-processing algorithm to measure important physical properties of lubricants. This sensor can measure three independent physical properties: viscosity, density and dielectric constant. This is significant technology because the direct measurement of a lubricant’s physical properties can provide important information about changing lubricant and engine health.

The miniature sensor allows for innovative packaging and strategic placement of the sensor in an engine to provide in-situ oil analysis without negatively affecting the design parameters of an overall system. The extremely fast response time and signal processing of the sensor allows for real-time measurement of lubricant properties.

According to Symyx, its solid-state resonator technology will operate in various types of fluid environments that experience a broad range of temperature, pressure, shock, vibration and fluid flow.

Symyx is actively pursuing companies interested in using or licensing this technology to measure and monitor the quality and condition of lubricants and other fluids. Already, several Symyx licensees of the sensor are commercializing the technology for use in the industrial and consumer markets. It is also currently being used in Symyx’ laboratories to measure the physical properties of gases and liquids.

Bosch GmbH Multifunction Oil Condition Sensor

Bosch is developing a multifunctional oil sensor that will determine oil level and oil condition. The oil level information will allow the oil dipstick to be omitted from the automobile.

Monitoring the engine oil condition is primarily intended to optimize oil drain intervals. However, it also provides increased insight into the actual state of the engine, which enables the possible detection of approaching engine failures or change in lubricant quality. The oil condition sensor will constantly measure the oil’s viscosity, permittivity, conductivity and temperature. The measured viscosity and permittivity (or dielectric constant) are the primary values supporting the oil condition evaluation. Commonly, chemical oil deterioration is associated with an increase in viscosity, whereas mechanical wear (shear) and fuel dilution lead to a decrease in viscosity.

A novel microacoustic device determines the viscosity. This device utilizes the piezoelectric effect to electrically excite high-frequency mechanic (or acoustic) vibrations at a sensitive surface. When this sensitive surface comes into contact with the oil, the electrical device parameters, such as oscillation frequency and damping, are changed according to the oil’s mechanical properties, especially viscosity. Thus, the viscosity can be electrically detected by measuring these parameters. In contrast to conventional viscometers, which are commonly used in laboratory applications, the microacoustic sensor does not contain any moving parts. Furthermore, due to its small size, it can be easily incorporated into the multifunctional oil-level and condition sensor.

Bosch’s multifunctional oil sensor is suitable for spark-ignition and diesel engines.

Eaton Corporation Fluid Condition Monitor

Eaton has developed a unique fluid condition monitor (FCM) technology that can monitor multiple fluid properties. The Eaton FCM is an in-situ real-time sensor based on impedance spectroscopy - a technology that measures multiple electrical properties of a fluid. It uses very small alternating current (AC) signals, which do not permanently disturb the fluid or the electrodes used in the measurement. Eaton’s FCM technology is differentiated by two critical attributes: it measures surface properties of the fluid in addition to bulk properties, and it has more degrees of freedom to enable the independent tracking of multiple lubricant parameters.

Measuring bulk properties reveals information about the conductivity (concentration and charge of ions) and dielectric constant (size, shape, and polarizability of the base fluid and its additives). Measuring the surface properties provides a quantitative measure of the physical and chemical properties of a fluid at the fluid-to-metal interface. This is a powerful technique when it is correlated to the real and measured physiochemical property changes occurring in aging or stressed motor oils.

The current prototype sensors are oil pan-mounted and include temperature-sensing capability. A small electronic module is used for signal conditioning, data capture and analysis.

Automotive Sensor Technologies Explained

Capacitance Method

A capacitor consists of two conducting plates separated by an insulating material called a dielectric. In the case of oil condition sensors, the oil is the insulating fluid. Capacitance is dependent on the surface area of the plates, the gap between the two plates and the insulating material. As the oil degrades, the capacitance measures this change. Capacitors store charge over time. Similar to filling a bucket with a hole at the bottom, it provides pressure on the hole when it is full. A capacitor takes time to fully charge and it also takes time for it to discharge. When it is fully charged, voltage is provided across the capacitor.

Dielectric Constant

A dielectric is an insulator. Dielectric constant is the rate of electric flux density produced in a material to the value in free space provided by the same electric field. This technique is able to detect when a change has occurred in the oil that alters the oil’s dielectric properties. These include oxidation, water, acids, mixed fluids and wear debris. There are only subtle differences between the capacitance and dielectrict constant methods.

Electrochemical Bead Matrix Method

This is a proprietary technique that employs a polymeric bead matrix (held between two conducting permeable surfaces) containing charged groups that serve as a conductive medium for measuring the solvent properties of oil. This method also works similar to the way a battery works. Milligram-sized charged resin beads are contained between two conducting surfaces separated by a nonconductive medium. The charged groups of beads (composed of both anions and cations) adjust to form an electrochemical bridge of varying strength depending on a relative change in the polarity of the oil. Because engine oils are relatively nonpolar and the beads are ionic, the beads do not form a conductive bridge. As the oil starts to degrade or become soot contaminated, the fluid becomes more polar (conducive to ionic interactions) and a bridge begins forming. This relative change in conductivity or capacitance is then measured between the two conducting surfaces.

Algorithm Method

This method uses mathematical models based on research to determine the optimum oil change intervals. Conditions like fluid temperature, speed, time and other critical factors are monitored and incorporated into the algorithm. Because the method does not actually test the condition of the oil, it cannot test for engine damage, coolant leaks, etc.

Acoustic Waves Method

See description of Bosch’s Microacoustic Sensor above.

Dielectric Loss Factor

See description of Lubrigard’s Oil Condition Sensor above.


Automotive oil condition monitoring is far from a mature technology. As this technology progresses and becomes more popular in the automotive industry, there will be many generations of sensors developed to improve accuracy and range of capability. While some vehicles come standard with oil change technologies today, the majority do not. The companies developing these sensor technologies must be able to convince the automotive industry and the public of their general reliability and value. If this is successful, we may see condition-based oil changes become the latest trend in vehicle technology over the next few years.

Special thanks to Joe Hedges with Voelker Sensors Inc; Ronald Johnson with Eaton Corp.; and Jeryl Hilleman and Mark Ulrich with Symyx Technologies.


  1. Capacitive Measuring Principle to Control the Oil Condition. (2003, May 12). Retrieved September 25th, 2003 from Continental Temic.
  2. Fitch, James C. (2003). How to Select a Motor Oil or Filter for Your Car or Truck. Tulsa, Okla.: Noria Corporation.
  3. How does FSS, the Mercedes-Benz M-Class Flexible Service System, Work? (n.d.). Retrieved September 25, 2003 from
  4. Intellek Oil Condition Sensor. (n.d.). Retrieved September 25, 2003 from Delphi Corporation Web site:
  5. Oil Level Sensor and Oil State Sensor. (n.d.). Retrieved October 3, 2003 from Bosch Web site
  6. Pecuniary Inc. Engine Oil Sensors and Extended Drains. (n.d.) Retrieved September 25, 2003 from
  7. Schwartz, S. E. and Smolenski, D. J. Development of an Automatic Engine Oil-Change Indicator System. SAE Paper 870403.
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About the Author

Jim Fitch, a founder and CEO of Noria Corporation, has a wealth of experience in lubrication, oil analysis, and machinery failure investigations. He has advise...