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I want to know if the methods a vehicle decides when to turn on the oil change light have to do with the qualities of the motor oil used in the last oil change. I have heard that the vehicle's computer calculates when the oil change light turns on due to number of engine startups, average speed of trip, time before thermostat opens. Now all of these (are there more?) can not infer the quality of oil engine with a possible except to the time it takes for the thermostat opening which may be a slight way to indirectly infer the type of oil last used.

I ask this question because supposedly synthetic motor oil lasts longer than conventional and if that is true I might wait longer after the oil change light turns based on my knowledge of how many hard/highway miles I have put on my vehicle.

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How the change oil light works is dependent on the make / model / year. –  Mark Johnson Dec 15 '11 at 0:33
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2 Answers 2

up vote 9 down vote accepted

I found a reference pdf for GM's Oil Life Monitor System.

How does the system work? The GM Oil Life Monitor System is not a mileage counter. It is actually a computer based software algorithm that determines when to change oil based on engine operating conditions. There is no actual oil condition sensor. Rather, the computer continuously monitors engine-operating conditions to determine when to change oil. Over the years, millions of test miles have been accumulated to calibrate the system for a variety of vehicles. The system was first introduced in 1988 and is now on more than 10 million GM vehicles.

also

Do I have to use special oil? The GM Oil Life Monitor System is calibrated for use with standard “Starburst” mineral- based automotive engine oil. Synthetic oils are not required except for the Corvette. Make sure to read the owner’s manual and select the viscosity and oil grade that is correct for your engine. Any oil selected for use should carry the ILSAC “Starburst”.

Thus it appears the Oil Life Monitor System does depend on which type of oil you use for it to give an accurate reading.

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Not all cars have an actual life monitor. My 2010 honda fit for instance counts down a combination mileage, and engine load resulting in 8.5K->9.5K mile oil changes. Both of which are in tolerance for the manufacturer. –  Chris Jan 23 '13 at 4:55
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I don't know about newer cars, however in older cars the "check oil" light is far less complicated - there is simply a sensor somewhere inside the engine block which turns the check oil light on if the oil goes below a certain level. At times when the oil in my engine has been low I've noticed that the light turns on and off (or even flickers) depending on whether I'm driving up or down a hill.

I've not got any direct experience with newer cars, but I can't see how it would be able to detect what type of oil is being used - my suspicion would be that it is based on engine use, mileage and the last time that the light was reset.

Depending on your car you may find that there is a manual reset procedure that you can use to reset the light without needing the use of the manufactures diagnostic tools, for example see How to Reset Change Oil Light on GMs, Chevrolet for a method which supposedly works for GM vehicles.

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