Oil Life Monitor -- How Does It Know?

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    Oil Life Monitor -- How Does It Know?

    Oil Life Monitor --
    How Does It Know?

    How long will oil last in an engine? What
    reduces the oil’s effectiveness? When should
    it be changed?
    Lubrication engineers perform a number
    of tests to answer these kinds of questions.
    Vehicles are operated under prescribed conditions,
    and periodically a sample of the oil is
    taken into the laboratory for analysis. When
    the condition of the oil is no longer satisfactory,
    the mileage is noted.
    From controlled testing like this, engineers
    in the past have determined two sets
    of mileage numbers, one number for normal
    driving and the other for severe conditions.
    Severe conditions can mean that the vehicle
    is driven hot (for example, pulling a trailer up
    a mountain) or is driven such that the oil
    never warms completely (for example, trips
    less than 5 or 10 miles in a winter climate). It
    is then up to the owner to decide whether
    their own driving is normal or severe and to
    change the oil accordingly.
    Now, science and technology have found
    a way of taking the guesswork out of the picture.
    GM is installing an oil life monitor in an
    increasing number of new vehicles. Using a
    simple indicator lamp or readout on the
    instrument panel, this system notifies the driver
    when to change the oil.

    Straight oil is not an ideal lubricant in an
    engine. A package of additives is needed to
    give the oil properties it does not naturally
    have or to enhance its natural properties.
    Some of the tasks accomplished by additives:
    - viscosity modifiers, to keep the oil the
    proper thickness over a wide range of
    operating temperatures
    - anti-oxidant, to keep the oil from
    - corrosion inhibitors, to protect
    engine components
    - anti-wear
    - anti-foam
    - detergents, to suspend solid particles.

    What Makes Oil "Wear Out?"

    Water in oil, resulting from extreme short-trip
    driving, photographed through a transparent
    oil pan.

    If you were to start out with a crankcase
    full of fresh, clean oil, and drove the vehicle
    for a period of time, eventually the oil would
    have to be changed. During this time, what
    can change fresh oil into "worn out" oil?
    First, dilution. When gasoline is burned in
    the combustion chamber, the by-products
    include a lot of water. Some of this water can
    find its way into the crankcase through piston
    ring blow-by. If the engine is cold, and if combustion
    is not perfectly complete, a small
    amount of acid is formed. It, too, can blow-by
    into the oil. You don’t need to be a top-notch
    scientist to realize that water and acid aren’t
    good things to pump through the lubrication
    system of the engine. If an engine is run long
    enough for the engine oil to warm, the water
    and acids will evaporate and not accumulate.
    But, during very short trips in cold weather,
    water and acids can enter the engine oil and
    cause the oil to "wear out."
    Second, the degradation of the oil and its
    additives. We mentioned earlier that a number
    of additives are put into oil to improve its
    performance. If these additives are degraded
    or decomposed, the oil is no longer capable
    of doing all of its jobs properly. Oil with
    degraded additives can become thick and
    dark. Additives become degraded by exposure
    to extreme heat. There are two places a
    lot of heat can reach the oil. One is near the
    combustion chamber. Oil at the top piston
    ring is exposed to very high temperature.
    And some bearing surfaces can also put a lot
    of heat into the oil at high operating temperatures.
    So, degradation of additives from high
    temperature operation is the second factor
    that can cause oil to "wear out."

    How Can Operating
    Conditions be Used to Predict
    Oil Life?

    Using carefully controlled laboratory
    tests, it’s possible for lubrication engineers to
    measure how long it takes to dilute engine oil
    during cold operation. And it’s possible to
    measure how long it takes for high temperature
    to degrade the additives.
    We usually think of measuring time in
    hours and minutes, but for an engine, the
    amount of revolutions it has run is also a
    good measure. So for the purposes of oil life,
    time is measured in engine revolutions.
    Engineers like to talk in terms of models.
    A model is a way to describe something
    mathematically. It’s possible to create an oil
    life model that very carefully matches the
    results of analyzing the oil in a laboratory.
    The oil life monitor, then, is based on a
    model. A computer chip in the Powertrain
    Control Module is loaded with a certain number
    of engine revolution counts. The count
    for each engine/vehicle combination is determined
    by testing. As the engine runs, each
    revolution is subtracted from the remaining
    count in the oil life monitor. When the count
    reaches zero, the instrument panel light
    comes on. But, here’s the clever part. When
    the various input sensors detect that the
    engine is running under either cold or hot
    conditions, it subtracts extra counts (penalties)
    for each engine revolution. So, the conditions
    that cause the oil to "wear out" make
    the counter run down faster.
    When the oil is changed, it’s necessary to
    reset the oil life monitor and the
    countdown begins again.
    NOTE: Synthetic oil resists "wearing out"
    better than mineral oil, so the oil life monitor
    is set to account for this, but only on vehicles
    that are specified for synthetic oil from the
    factory -- the Corvette, for instance. Using
    synthetic oil in other vehicles is certainly not
    harmful, but the oil life monitor will continue
    to count down as though the engine contained
    mineral oil.

    Special thanks to TeckLink 3/2002
    Special thanks to - Shirley Schwartz

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    AJxtcman's Avatar
    AJxtcman is offline Cadillac Owners Connoisseur
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    Thread Starter

    Re: Oil Life Monitor -- How Does It Know?

    GM Oil Life System Revisited
    Briefly, engine oil degrades in a
    predictable fashion, according to several
    measurable engine operating conditions.
    The engine control module counts
    combustion events (measured in rpm)
    and reads coolant temperature. From
    these numbers, the computer is able to
    track oil deterioration and notifies the
    driver when a change is needed.
    The best value from the cost of an oil
    change is obtained by maximizing the
    mileage between changes, so long as
    there is no adverse effect to the engine.
    With the GM oil life system, the average
    person can expect oil change intervals of
    4000-7000 miles for mixed driving, and
    7000 to 10000 miles for highway driving,
    while the Chevrolet Corvette and the
    2002 Envoy, Bravada and TrailBlazer can
    achieve 15000 miles under ideal
    Since the GM oil life system first
    appeared on some 1988 Oldsmobiles,
    over 10 million have been built,
    presently at the rate of over 3 million a
    year. By model year 2003,
    GM expects to install oil life
    systems on essentially all
    cars and light duty trucks.
    This past May, the GM
    oil life system development
    team was honored by
    receiving the first ever
    Environmental Excellence
    in Transportation award
    from the Society of
    Automotive Engineers. This
    award recognizes that the
    extended range offered by
    the oil life system can save
    huge amounts of new oil,
    and can keep thousands of
    gallons of used oil out of
    the environment.
    There’s a lot of information on vehicle
    maintenance shared on consumeroriented
    websites – some correct, come
    erroneous, and some simply outdated.
    For instance, conventional wisdom calls
    for oil changes every 3000 miles. Not
    surprisingily, this conservative figure is
    also supported by those who derive
    income from selling oil changes. Many
    of your customers have become
    convinced that any longer oil change
    interval is somehow harmful to their
    At the retail level, you can do your
    part by promoting proper use of the GM
    oil life system. Become familiar with its
    function, and be prepared to help
    customers understand that observing
    the montor’s recommendation is the
    easiest way to take the guesswork out
    of oil change intervals. It also ensures
    that they are giving their vehicle the
    proper care it deserves, at the minimum

    Special Thanks to David Staley and Chuck Burns
    Special thanks to Techlink ---- 11/2001
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    AJxtcman's Avatar
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    Thread Starter

    Re: Oil Life Monitor -- How Does It Know?

    GM Oil Life System Revisited #2

    How often should engine oil be changed?

    - 3,000 miles
    - 5,000 miles
    - 7,500 miles
    - 10,000 miles

    Actually, all of these are correct, depending on operating conditions. Oil life is affected by many factors other than just miles driven. The type of driving, temperature, and engine load all play a part.

    That’s why GM has developed the GM Oil Life System, an electronic watchdog that keeps track of all these variables and notifies the driver when it’s time to change oil. We first told you about the GM Oil Life System in the March 2000 TechLink. Since then, the system has become standard equipment on nearly all GM products.

    Briefly, the Oil Life System is programmed with a certain number of engine revolutions. As the engine runs, this number is reduced until it reaches zero, and the Oil Life light or message comes on. But there’s more. Operating the engine under low or high temperatures, and under high load conditions subtracts (penalizes) extra revolutions, so the light comes on sooner.

    Changing engine oil according to actual need rather than an inflexible schedule provides several benefits.

    First is simpified determination about when to change oil. No more decisions about “normal” conditions vs. “severe” conditions. Second is reduced operating costs for GM’s customers, who now have to change oil only when it’s needed. Third is minimizing the amount of used oil that must be disposed of. And fourth, engines will always be running with sufficiently fresh oil, for long life.

    These benefits will be realized only if engine oil is actually changed as indicated by the GM Oil Life System.

    Some customers “get it” when it’s explained to them. Others may be reluctant to deviate from traditional oil change interval charts. So, part of the responsibility falls on retail service people to help get the message out.

    There’s More
    Traditionally, the vehicle maintenance schedule has been based on miles or time, while the oil change interval is now based on the GM Oil Life System. This could result in customers having to bring their vehicles in for an oil change when the light comes on, only to find that the vehicle is due in a month for scheduled maintenance.

    That’s all changing. In the accompanying article “Simplified Maintenance Schedules”, you’ll learn how maintenance intervals are now being tied into the oil change intervals indicated by the Oil Life System.
    Sepcial Thanks to Jerry Garfield and Chuck Burns
    Special Thank to TechLink 5/2003
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    AJxtcman's Avatar
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    Join Date
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    Thread Starter

    Re: Oil Life Monitor -- How Does It Know?

    GM Oil Life System, One More Time #3

    Where do you stand on the following issues?
    1. Do you want to continue to build customer loyalty and grow your business?
    2. Do you want to show your customers you truly have their best interests at heart?
    3. Do you want to help improve the environment?
    4. Would you like to quit being a part of the throw-away generation?

    GM’s development of the Oil Life System and its relationship to the new Simplified Maintenance Schedule have a direct bearing on how well you can answer YES to all of these questions.

    How the Oil Life System Works
    We’ve explained the GM Oil Life System (GMOLS) in detail before (March 2000, May 2003) so this is going to be brief.

    GMOLS is a computer-based algorithm that assesses engine combustion events, temperature, vehicle use, and other parameters to determine optimum oil change intervals. Oil changes are now called for when actually needed, instead of depending on generic time or mileage interval tables. Mild highway driving in a mild climate can yield change intervals of 7,000 miles (11,000 km) or more, and as high as 12,000 miles (19,000 km) for some vehicles. Short trip driving in cold weather may reduce intervals to 3,000 miles (5,000 km) or less. Most people driving a combination of city and highway will likely see intervals of about 6,000 miles (10,000 km).

    When GMOLS determines that an oil and filter change is needed, the driver is notified by a Change Oil message on the instrument panel. Oil should be changed within 600 miles (1000 km).

    TIP: The Oil Life System must be manually reset when the oil is changed.

    How the Oil Life System is Related to Maintenance
    The previously complicated, traditional normal/severe maintenance schedules required about 25 pages of explanation in the owner’s manual. The new simplified maintenance schedules can be explained in about 3 pages.

    All routine maintenance is grouped into one of two schedules, Maintenance I and Maintenance II. These services should be performed alternately, each time the GMOLS message is displayed.

    Benefits of GM Oil Life System and Simplified Maintenance
    Benefits for the customer -- GMOLS takes the guesswork out of when oil changes are needed; the owner doesn’t have to keep track of anything. With maintenance intervals now aligned with oil changes, the customer can conveniently have both done during one service visit.

    Benefits for the dealer -- Because of the typically extended oil change intervals, the customer may come back less frequently. But when they do come back, it’s for more services. The inspection and service points of both Maintenance I and Maintenance II are thorough, and are intended to keep the vehicle in good working order. They also give the technician the opportunity to locate, identify and recommend other needed services.

    Benefits for the environment -- With GMOLS now installed on upwards of 20 million vehicles, if it’s used as intended, it can save almost 100 million gallons of oil in 5 years. And remember that every quart of oil poured into an engine eventually has to be drained out and properly disposed of.

    What’s Next?
    In the next few months, GM is going to saturate owners with information about the GMOLS. Radio interviews, TV talk shows, magazines, newspapers, the internet and dealership kits will all be used to promote a proper understanding of GMOLS and its benefits, and to promote its proper use. GMOLS was also promoted at the National Auto Dealers Association (NADA) convention in January of this year.

    How Can You Prepare?
    Because of GM’s media efforts, owners are going to become familiar with GMOLS. It’ll be a good idea for you to get yourself up to speed as well.

    Literature and Materials -- GMSPO is making Oil Life System promotional material available through several sources. You can download service reminder letters and maintenance schedules at . GMSPO-approved vendors have a wide selection of new service reminders including a message about GMOLS. A kit including poster, consumer brochures, and counter display is available from .

    Maintenance Reminder Stickers -- Traditional stickers provided a place to write the date and/or mileage for the next oil change. To encourage use of the Oil Life System, a new maintenance reminder sticker says the Change Oil Light indicates a need for maintenance. It provides a place to check off whether the next service should include Maintenance I or Maintenance II, plus the date and mileage of the last maintenance performed.

    Special Thanks to Chuck Burns
    Special Thanks to TechLink 3/2004
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