Tech Stuff

Can We Trust Oil Life Monitors?

This Honda Pilot was overdue, but the motorist just kept driving.
<p>This Honda Pilot was overdue, but the motorist just kept driving.</p>

If you ask most automotive technicians if they trust an oil life monitor, or OLM, they will typically say “no way” and the reasons for this view will come fast and furiously.

But the manufacturers are equipping just about all of their models with some form of OLM. But two questions often come up: “Can an OLM light or system accurately tell a customer when they need an oil change?” and, “Can an OLM be trusted?”

The short answers are yes, but there are a vast number of variables that need to be taken into consideration, and both the customers and service technicians must be actively involved. The proper engine oil and the engine oil level must be maintained along with closely following the operator’s manual.

The constant improvement in engine technology, manufacturing processes, engine management systems, engine lubricants, computerization and other factors such as the Corporate Average Fuel Economy (CAFE) requirements have for the most part rendered the 3,000-mile oil change service interval obsolete. The modern engine oil additive package prevents sludge and varnish formation, and does this while protecting against engine wear and loss of engine performance longer than previous oils, even under increasingly severe engine operating environments.

Many of today’s original equipment manufacturers (OEMs) routinely recommended oil change intervals of 5,000 to 8,000 miles and beyond. Combining these advances in technology with an OLM helps to remove some of the guesswork and concerns that a driver was previously faced with when it comes to a required oil change.

Even today’s best engine oil has a fixed or limited lifetime and will need to be replaced or maintained periodically to ensure the safety, longevity and reliable performance that customers demand from their vehicles. Unfortunately, it seems that maintaining a vehicle isn’t something that is commonly a top priority for today’s busy motoring public.

Increasing the oil change service interval is something drivers want. It reduces vehicle down-time and decreases the operating costs, something the manufacturer can promote about their vehicle line. It also prevents the draining of oil that has not reached the end of its service life.

These are examples of oil life monitor displays on several different vehicle dash displays.
<p>These are examples of oil life monitor displays on several different vehicle dash displays.</p>

Today’s manufacturers will recommend scheduled oil changes in the owner’s manual. A vast number of different driving conditions and other variables that affect oil life and engine performance will be considered when creating an effective timetable that will call for maintenance before signs of engine wear occur.

But following the owner’s manual will lead to a generalization of when an oil change is needed. Yes, the owner’s manual should be followed closely. But when you look at the owner’s manual it may state that an 8,000-mile oil change interval is OK under normal or ideal operating conditions. But just what are these ideal operating conditions? And if the vehicle is operated under non-ideal operating conditions, how is this going to affect the engine’s oil and the oil’s life or condition?

Many drivers think that their vehicles operate under ideal conditions, and thus justifying extended service intervals, when in fact they are operating under severe conditions in respect to the oil in the crankcase and need more frequent oil changes. Stop-and-go driving, frequent short trips, very cold or very hot weather generally fall into the severe category.

But many vehicles operate in a mix of conditions and this is where the confusion starts. This confusion is what the OLM is supposed to eliminate. Today’s OLM will take into consideration many of the factors that commonly shorten the oil change interval. These include but are not limited to:

  • Short trips, especially in freezing weather.
  • Frequent stop and go situations.
  • Dusty or extreme hot weather conditions.
  • Turbo-charged engines.
  • Flex fuel operation.
  • Towing/heavy-duty operation.
  • High mileage engines or engines that are burning oil.

These scenarios contribute to oil contamination from water, fuel, dirt, excessive blow-by gases, corrosive acid forming agents, oil oxidation, sludge, volatility issues, viscosity shearing problems, premature failure of the oil’s additive package and a host of other issues which all tend to shorten a required oil change interval.

But there are circumstances that can lengthen or extend an oil change interval:

  • Current engine control technology.
  • The use of synthetic engine oil.
  • Better oil filter filtration.
  • Oil sump capacity.
  • Predominantly highway driving.
  • Environmental waste concerns.

Today’s engine management systems keep fuel control as close to stoichiometric as possible even under acceleration, limiting fuel contamination. Synthetic lubricants provide exceptional oxidation stability, thermal constancy and shear stability. Superior quality oil filters limit the amount of wear and other foreign materials in the engine oil.

Highway operation allows the engine to reach operating temperature at a reduced rpm, vaporizing any water and fuel in the oil; it also lowers the operating hours per mile traveled. Reducing the impact of the waste oil that is created is also a crucial factor, not just for the environment but for consumers and manufacturers alike.

The use of an OLM can take all of these scenarios and more into consideration and can adjust the oil change service interval accordingly.

There are currently four different versions of OLM being used and each has its own operational characteristics. Some OLM’s are more sophisticated, or intelligent, than others, but they will typically take into consideration the factors that can affect the engine oil life in both a positive and negative way.


The proper oil must be installed in the engine that meets or exceeds the manufacturer’s specification, for the OLM to work as intended.
<p>The proper oil must be installed in the engine that meets or exceeds the manufacturer&rsquo;s specification, for the OLM to work as intended.</p>

Method #1: Measuring the distance

This is the most basic form of OLM. This OLM merely keeps track of the distance driven since the last oil change. When the predetermined distance is reached a warning light or message reminder is illuminated warning the driver that an oil change is due. Manufacturers such as Honda, Toyota and Hyundai use this system.

Hyundai’s system counts down the distance and will display a “SERVICE IN” miles each time the ignition is switched on. This style OLM is strictly keeping track of the distance since it was reset, and most will also track negative miles once it reaches zero. After the Hyundai system reaches zero it will display “SERVICE REQUIRED” as the message to the driver.

The distance-measuring OLM does not take any driving factors into consideration. Short trips, long highway operation, towing, weather conditions and other factor that affect oil life are not taken into consideration with this system.

This may mean that the distance-style OLM light may not be effective at predicting the actual wear conditions of the oil in both a negative and positive way.

Lightly driven vehicles may get their oil changed far too often and heavy, hard, hot-driven vehicles towing a trailer may not get the oil change that is needed soon enough.

These are two examples of Mercedes-Benz and a Jaguar oil level, temperature and quality sensors.
<p>These are two examples of Mercedes-Benz and a Jaguar oil level, temperature and quality sensors.</p>

It’s because of this lack of sophistication that this style of OLM relies heavily on the vehicle operator to ensure that the oil level is maintained at the correct level and manufacturer recommended oil was installed and, most importantly, that the vehicle operator check the suggested service intervals in the owner’s manual for their driving conditions.

Method #2: Tracking vehicle operating conditions

This style of OLM is software-based and uses complex math or algorithms to better predict when the engine oil will need to be changed. This system is continually tracking how the vehicle is being operated and under what conditions.

General Motors (GM) started using this type of OLM (GM calls it GM Oil-Life System, or GMOLS) back in 1998 and based the need for an oil change heavily on the number of engine revolutions and operating temperature.

GM studied the average vehicle driving conditions and decided on four classifications: normal flowing highway, high temperature/high load situations, city driving/short trips and cold starts and extreme short trips.

GM’s research showed that engine oil degrades primarily related to oil temperature. In the first three operational categories, oil wear was related to operating temperature and that extreme short trips, the final operating category, generated enough water and oil contaminates to cause the oil to degrade (temperature related: lower oil temperature = high contamination).

Using this information and data from many other sensors on the vehicle, the software will routinely adjust the oil change interval based on operational characteristics, climate conditions and driving habits.

Ford’s Intelligent Oil Life Monitor (or IOLM) is also a software-based OLM that calculates when an oil change is required — very similar to the GMOLS, but the Ford system incorporates a timer that will turn on the oil change required light after one year has passed. Fiat-Chrysler also uses the software-based method and their calculations account for the amount of ethanol in the fuel being used.

All current engine oil has a fixed life span and will eventually need to be changed.
<p>All current engine oil has a fixed life span and will eventually need to be changed.</p>

Both Ford’s IOLM, GM’s OLM and Fiat-Chryslers OLM monitor depend on the correct oil being installed, the proper oil level being maintained and that the OLM system is reset after an oil change is performed.

Method #3: Measure the engine oil temperature and level combined with vehicle operating conditions

Most manufacturers agree with GM’s findings: Engine oil degradation is largely affected by its temperature.

VW/Audi uses an OLM that calculates the engine oil’s thermal load using an oil level/temperature sensor in combination with a fuel consumption and mileage/time algorithm to calculate when an oil change is necessary. This differs from GM and Ford fully software-based system in that the OLM measures the amount of oil and its temperature in the crankcase continuously while the engine is running. By measuring the level of oil in the crankcase, this style of OLM can take into consideration the accelerated wear that occurs to the engine’s oil and its additive package when the engine oil level drops below the full mark or farther.

When VW/Audi started using this OLM they also changed the standard oil that was installed in their engines, moving to a more robust synthetic engine oil to enable an extended service interval.

Method #4: Measuring the actual oil condition combined with vehicle operating conditions

Measuring the distance, using a software-based algorithm and monitoring the oil’s temperature and level are all worthy ways of safely extending a vehicle’s oil change interval, but they all have one common shortfall: They can’t directly measure the condition of the engine’s oil or detect contaminates in it.

However, a sensor that could monitor the actual engine oil condition was developed. These oil condition sensors take advantage of the fact that the dielectric properties of engine oil change as it wears out, breaks down or contamination builds up.

These sensors are even capable of detecting the depletion of the oil’s additive package as the oil’s acidity increases and can identify engine coolant or fuel in the oil.

Mercedes-Benz takes advantage of an oil condition sensor in its Flexible Service System (FSS) or ASSYST systems to extend the oil change intervals of these vehicles. BMW also uses a similar sensor to evaluate the actual condition of the engine oil and extend oil services on their models.

Quite a variety! Here are oil samples at a Chevron testing facility. Photo courtesy of Chevron Corp.
<p>Quite a variety! Here are oil samples at a Chevron testing facility. Photo courtesy of Chevron Corp.</p>

The oil condition sensor is allowing extended service of upwards of two years and 15,000 miles if the proper oil is installed.

When an oil sensor is used in combination with operating condition data, and oil level and temperature, the extended service interval can be easily and safely reached but only when the proper manufacturer’s oil is installed, and the correct level is maintained.

Major factors affecting the use of an OLM and achieving proper engine life and durability

Oil quality is a major factor in the proper functioning of all OLM systems.

Some OLM systems can physically measure the oil’s condition, but the OLM can’t compensate for sub-standard engine oil or an engine oil that does not meet the minimum preference standards set out by the OEM.

An inferior engine oil may reach the end of its life, thermally breaking down, oxidizing, forming engine deposits and sludge, all while the OLM indicates substantial remaining life.

This engine oil degradation can accelerate engine wear, reduce performance and reduce engine durability and longevity. Another major factor is driving conditions — short trips, stop-and-go, dusty, extreme hot or cold and towing situations.

Most of these operating conditions will fall under the severe service definition in the vehicle’s owner’s manual, something that needs to be taken into consideration with some forms of OLM, especially the simpler mileage counter style.

Can we trust an OLM?

Yes, today’s OLM can be trusted, when they are used in conjunction with an engine oil that meets or exceeds the manufacturer’s recommendations. The OEMs have developed and validated their OLM algorithms in conjunction with analytical oil tests and research.

This research ensures that even at the maximum drain interval, the engine oil will continue to meet all functional requirements.

Extended oil change intervals have benefits valuable to the customer; less frequent service requirements, less down time, reduced operating costs and more environmentally friendly operation due to less waste oil and superior filters.

The use of an oil condition sensor and oil level sensor has eliminated the need for a dipstick on some vehicles, something that symbolizes the fact that fewer people are opening their hoods to inspect the engine’s oil level.

The extended oil service interval is a fact of life, and we will likely see the intervals grow longer. As modern engines rely on engine oil technology to do more, the price if an oil change will increase.

Engine oil and its additives are continually improving, as are engine technology, oil filtration and engine design. The OLM will evolve as well, taking these and other factors into consideration as it decides how the engine oil degrades.

Many manufacturers have also increased the amount of oil in the engine to compensate for longer service intervals. As an example, a 2018 5.3 V8 Chevrolet Silverado now holds 8 quarts of 0W20, an increase from the 6 quarts a 2014 model held. But all OLM systems, from the simple distance counter to the complex oil condition system, are dependent on the proper manufacturer-specific engine oil being installed during an oil change and that the correct oil level is maintained throughout the service interval. If neither of these requirements is met, the OLM system can’t function as planned. ■

I would like to thank Sean Lantz, mechanical engineer and products technical specialist with Chevron Lubricants, for his valuable contributions to this article.

Jeff Taylor boasts a 34-year career in the automotive industry with Eccles Auto Service in Dundas, Ontario, as a fully licensed professional lead technician. While continuing to be “on the bench” every day, Jeff is also heavily involved in government focus groups, serves as an accomplished technical writer and has competed in international diagnostic competitions as well as providing his expertise as an automotive technical instructor for a major aftermarket parts retailer.

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