Rick's Free Auto Repair Advice

Oil life monitor

How does the oil life monitor work?

Most cars and trucks now have an oil life monitor system that tells you when to change your oil. Many people think it just clocks your mileage. It doesn’t. It’s far more sophisticated than that because determining the life of your oil depends on many more factors than just miles. Driving in stop and go traffic, long periods of idling, driving for long periods in hot weather or lots of cold weather starts wears out your oil faster. So oil life monitor system track how you operate your vehicle.

The oil life monitor doesn’t use a sensor to determine oil condition

People think that the oil life monitor system relies on some type of sensor that detects oil condition. There is no such sensor. Instead, the system tracks your actual driving habits and uses an alogrhithym to determine how your driving affects oil life.

Starting with the 2010 model year, GM instituted an oil life monitor that calculates remaining oil life based on the factors listed below. The algorithm assumes that you’ve used the correct DEXOS oil and viscosity as recommended in the owner’s manual AND assumes that you check and maintain the proper oil level vw warning icons low oil pressure lightat all times. If you use a non-DEXOS oil, wrong viscosity or let the engine run low on oil, the oil life monitor will no longer be accurate and you risk driving too long between oil changes.

What the oil life monitor tracks

After each oil change reset, the GM oil life monitor tracks

• Engine revolutions- The GM oil life monitor starts with a factory preset number of engine revolutions stored in memory. Every time the engine is started and run, the oil life monitor tracks the number of revolutions run and subtracts those from the factory programmed target.

• Engine temperature— The algorithm incorporates multipliers that reduce the number of engine revolutions and thus remaining oil life, based on how far engine oil temperature varies from normal oil temperature. If the PCM records an engine temperature above 260°F, the remaining oil life will immediately show 0% remaining life. Cold starts reduce oil life and the algorithm takes that into account by reducing the number of revolutions accordingly.

• Miles since last reset—The monitor records miles traveled since the last oil reset and maintains a MAXIMUM value of 7,500 miles for ALL 2013 and later GM vehicles (except the Volt) before it show 0% remaining oil life.

Time—The oil life monitor records the amount of time the engine runs since the last oil change reset. The time tracking is a liner measurement and decreases remaining oil life on a straight life basis in conjunction with the other tracked variables. The monitor will show 0% after one year regardless of miles driven, engine revolutions or time run.

Most carmakers have had to tweak their oil life monitor algorithms

“GM’s original OLM was not based on mileage; it used engine revolutions and temperatures to calculate the time between oil changes. The original systems could allow up to 19K (under ideal conditions) before an oil change. But that changed after GM started seeing timing chain failures and issues with some of its engines. The chains were stretching and turning on the check engine light – something a customer doesn’t like to see. In the worst cases, it led to engine failure.

Seeing a dramatic increase in warranty claims, the engineers decided that the OLM system needed to be recalibrated. Now GM’s OLM incorporates mileage in its calculations, and the company has lowered the maximum distance between oil changes to increase the life of the timing chain, and lower warranty claims.”— autoserviceworld.com July 12, 2016 by Jeff Taylor

When to change oil on a GM vehicle

Regardless of what self-proclaimed experts, oil distributors or oil companies may claim, the maximum oil life on GM vehicles (except for the Volt model) is 7,500 miles or less. Oil life depends on time, miles, temperature and engine revolutions. Do not be fooled into thinking you can go beyond this limit.

Factors that degrade oil and reduce oil life

Oil Oxidation reduces oil life

Oil contains anti-oxidant additives to combat oil breakdown due to oxidation. But as oil meets heat, foam and water, those additives get used up and the oil oxidizes, turning into sludge.

• Idling in slow traffic causes oil oxidation

• Cold starts with a rich fuel mixture causes raw fuel and water to enter the crankcase and mix with the oil, causing oxidation and breakdown.

• Turbochargers operate at very high heat. Driving at highway speeds and then shutting down the engine can oxidize the oil left in the turbo.

• Not checking oil level causes the remaining oil to work harder and use up its antioxidation additives much faster.

Engine overheating will deplete remaining oil life

If the engine coolant temperature exceeds 260°F, the oil life monitor will immediately to to 0% remaining oil life.

©, 2017 Rick Muscoplat



Posted on by Rick Muscoplat

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