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Discussion Starter · #1 · (Edited)
I just changed the oil, and in < 1 week and 30 miles the DIC shows the oil life percentage down to 94%. WTF! I’ve put on 5,800 miles since I last changed it (displaying 19% life remaining). Does anybody know how the oil life percentage is calculated? Clearly it must be more that simply time and/or milage. I do know that the percentage decreases substantially when I usually let in idle after remote start(s) during the winter. But this time it decrease by 6% with no R/S and hardly any miles.
 

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How the Chevrolet Oil Life Monitor (OLM) system works and what to expect
The Chevrolet Oil Life Monitor (OLM) system is not a simple oil quality sensor, but a software-based, algorithm-driven device that takes into account various operating conditions of the engine to determine when the oil needs changing. Certain driving habits can affect the life of the oil, as well as driving conditions such as temperature and driving terrain. Lighter, more moderate driving conditions and temperature will require less frequent oil changes and maintenance, while more severe driving conditions will require more frequent oil changes and maintenance. Read the table below to see how the OLM system determines oil life:

The oil life meter is located on the information display on the dashboard, and will count down from 100% oil life to 0% oil life as you continue to drive the vehicle, at which point the computer will trigger a reminder for you to “Change Engine Oil Soon.” Around the 15% oil life threshold, the computer will remind you that an “Oil Change Is Required,” giving you ample time to plan ahead to have your vehicle serviced. It is important not to wait to have your vehicle serviced, especially once the indicator reads 0% oil life. If you do wait and servicing is overdue, you risk severe damage to the engine - which could leave you stranded or worse. GM recommends that an oil change should be completed within two fuel tank fill-ups from when the first message was displayed.
 

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Discussion Starter · #3 ·
How the Chevrolet Oil Life Monitor (OLM) system works and what to expect
Read the table below to see how the OLM system determines oil life:
I tracked down the source article that was copied/pasted from so I could view the chart it mentioned, but the chart doesn't explain how my % dropped 6% in less than a week and 30 (light, flat) miles.
 

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I just changed mine last week and have about 700 Kms since. My monitor is sitting also at 94%.

Did you let most of the oil drip out and how much oil did you put in? Mine took 4.3 liters after I waited for the oil to stop dripping. Maybe it somehow figures out how much old oil remained with a translucent sensor or some kind of algorithm.
 

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Discussion Starter · #5 · (Edited)
After I loosened the filter and opened the valve (all four tires on flat ground), my neighbor stopped over and we chatted for at least 30 mins. The oil had long since stopped dripping before I proceeded to change the filter, close the valve and dump in 4.25q.

Just now, since the 5q jug still had 3/4q of new oil in it, I added it to the engine, marked off 3/4q on a transparent container and drained 3/4q into it. It wasn't pitch black, but it was certainly darker than 38 mile oil should be, maybe how 2-3,000 mile oil would look.

The only thing I can think of is...since I replaced the OEM plug with a ball valve, I'm thinking that it protrudes high enough into the pan that it prevents the last 1/2 cup or so of dirty oil from draining. And then that dirty remaining oil mixes with the fresh stuff. It could be that there is a sensor that detects contaminant density and/or transparency of the oil to use in its life calculations. I think next oil change I'm going to have to ditch that valve and put the OEM plug back in. It's a shame because it makes for a much easier and mess-free oil change. I may just remove it and cut off any excess length to insure it doesn't extend any higher than the pan threads.
 

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Good point. I jack the driver's side at the "K" frame bolt as high as the jack will go, it usually lifts the back tire about an inch from the ground tilting the pan towards the drain hole. This also leaves me plenty of room to go under and access the drain plug and inspect.
 

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Discussion Starter · #7 ·
Makes me wonder what the optimal drain angle actually is. It just looked to me like lifting one or both front tires would cause the oil to hide in the rear corner(s) of the pan. I may also experiment with that next time…after the dripping stops, raise/lower in an attempt to get more to start dripping again. Probably overkill, but, the more the better.
 

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The OLM cannot tell between new oil and bad oil. Below is an older expenlation of the OLM. It has been revised a few times since then but still operates much the same.

The GM engine oil life monitor counts engine revolutions and accumulates the number for the basis of the oil life calculation. It then adds deterioration factors for operating temperature, start up temperature, soak times, ambient, coolant temperature, etc... There are a LOT of factors that "adjust" or affect the slope of the deterioration but the fundamental deterioration is traced back to the ZDDP depletion that is inescapable with engine revolutions. The specific rate of ZDP depletion is readily measurable for any given engine so that is the fundamental item that is first calibrated for the oil life algorithm to tailor it specifically to that engine.

You would obviously like to get the oil out of the engine before the ZDDP concentration gets so low that it is ineffective at being at the right place at the right time and preventing engine wear so that becomes the long term limit on oil life for that application.

The other things that determine oil life such a acid build up, oxidation, petane insuluables such as silicon from dust/dirt, carbon or soot build up from the EGR in blowby, water contamination, fuel contamination, etc.... are all modeled by the multipliers or deterioration factors that "adjust" the immediate slope of the line defined by the engine revolution counter as those items can be modeled in other ways and accounted for in the immediate slope of the ZDDP depletion line.

The algorithm was developed over the course of many years by several lubrication experts at GM Fuels and Lubes, spearheaded by Doctor Shirley Schwartz who holds the patents (with GM) for the algorithm and the oil life montitor. I had the luck of working directly with Dr. Schwartz when the idea of the oil life monitor first progressed from the theoretical/lab stage to real world testing/development/validation. There were fleets of cars operated under all conditions that deteriorate the oil life for any and every reason and , thru oil sampling and detailed analysis of the oil condition, the algorithm was developed, fine tuned and validated to be the most accurate way invented yet to recommend an oil change interval by. As just one example, I have seen cars driven side-by-side on trips, one towing a trailer and one not, for instance, to prove the effectiveness of the oil life monitor in deteriorating the oil at a faster rate just because of the higher load, higher average RPM, higher temps, etc...and it works flawlessly.

The oil life monitor is so effective because: it is customized for that specific vehicle/engine, it takes everything into account that deteriorates the oil, it is ALWAYS working so as to take into account THAT INDIVIDUALS driving schedule, and it tailors the oil change to that schedule and predicts, on an ongoing basis, the oil life remaining so that that specific individual can plan an oil change accordingly. No other system can do this that effectively.

One thing is that I know personally from years of testing and thousands of oil analysis that the oil life algorithm works. There is simply no argument to the contrary. If you don't believe me, fine, but, trust me, it works. It is accurate because it has been calibrated for each specific engine it is installed on and there is considerable testing and validation of the oil life monitor on that specific application. NOt something that oil companies or Amsoil do. They generalize....the oil life monitor is very specific for that application.

Oil condition sensors in some BMW and Mercedes products are useful, also. They have their limitations, though, as they can be blind to some contaminates and can, themselves, be contaminated by certain markers or constituents of certain engine oils. Oil condition sensors can only react to the specific oil at that moment and they add complexity, cost and another potential item to fail. One other beauty of the GM oil life monitor is that it is all software and does not add any mechanical complexity, mass, wiring or potential failure mechanism.

There is considerable safety factor in the GM oil life monitor. Typically, I would say, there is a 2:1 safety factor in the slope of the ZDDP depletion curve....in other words, zero percent oil life per the ZDDP depletion is not zero ZDDP but twice the concentration of ZDP considered critical for THAT engine to operate under all conditions reliably with no wear. This is always a subject of discussion as to just how low do you want the ZDDP to get before the oil is "worn out" if this is the deciding factor for oil life. We would tend to be on the conservative side. If the oil life is counting down on a slope that would recommend a 10K change interval then there is probably 20K oil life before the ZDDP is catostrophically depleted....not that you would want to go there...but reason why many people are successful in running those change intervals.

Please...NOT ALL ENGINES ARE THE SAME. The example above is an excellent practical justification of why you would want to add EOS and change the 15W40 Delvac in the muscle car at 3000 miles max and yet can run the Northstar to 12500 easily on conventional oil. You must treat each engine and situation differently and what applies to one does not retroactively apply to others. This is where Amsoil falls short in my book by proposing long change intervals in most everything if you use their oil. It just doesn't work that way. You can run the Amsoil to 12500 with no concerns whatsoever in the late model Northstar because even the oil life monitor tells you that for conventional oil off the shelf. Would I do that to the 502 in my 66 Chevelle...NO WAY. Amsoil says I can though. Wrong.


There are entire SAE papers written on the GM oil life monitor and one could write a book on it so it is hard to touch on all aspects of it in a single post. Hopefully we hit the high spots. Realize that a GREAT deal of time, work and energy went into developing the oil life monitor and it has received acclaim from engineering organizations, petroleum organizations, environmental groups all across the board. It is not some widget invented in a week and tacked onto the car.
 

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Discussion Starter · #9 · (Edited)
The OLM cannot tell between new oil and bad oil. Below is an older expenlation of the OLM. It has been revised a few times since then but still operates much the same.

The GM engine oil life monitor counts engine revolutions and accumulates the number for the basis of the oil life calculation. It then adds deterioration factors for operating temperature, start up temperature, soak times, ambient, coolant temperature, etc... There are a LOT of factors that "adjust" or affect the slope of the deterioration but the fundamental deterioration is traced back to the ZDDP depletion that is inescapable with engine revolutions. The specific rate of ZDP depletion is readily measurable for any given engine so that is the fundamental item that is first calibrated for the oil life algorithm to tailor it specifically to that engine.

You would obviously like to get the oil out of the engine before the ZDDP concentration gets so low that it is ineffective at being at the right place at the right time and preventing engine wear so that becomes the long term limit on oil life for that application.

The other things that determine oil life such a acid build up, oxidation, petane insuluables such as silicon from dust/dirt, carbon or soot build up from the EGR in blowby, water contamination, fuel contamination, etc.... are all modeled by the multipliers or deterioration factors that "adjust" the immediate slope of the line defined by the engine revolution counter as those items can be modeled in other ways and accounted for in the immediate slope of the ZDDP depletion line.

The algorithm was developed over the course of many years by several lubrication experts at GM Fuels and Lubes, spearheaded by Doctor Shirley Schwartz who holds the patents (with GM) for the algorithm and the oil life montitor. I had the luck of working directly with Dr. Schwartz when the idea of the oil life monitor first progressed from the theoretical/lab stage to real world testing/development/validation. There were fleets of cars operated under all conditions that deteriorate the oil life for any and every reason and , thru oil sampling and detailed analysis of the oil condition, the algorithm was developed, fine tuned and validated to be the most accurate way invented yet to recommend an oil change interval by. As just one example, I have seen cars driven side-by-side on trips, one towing a trailer and one not, for instance, to prove the effectiveness of the oil life monitor in deteriorating the oil at a faster rate just because of the higher load, higher average RPM, higher temps, etc...and it works flawlessly.

The oil life monitor is so effective because: it is customized for that specific vehicle/engine, it takes everything into account that deteriorates the oil, it is ALWAYS working so as to take into account THAT INDIVIDUALS driving schedule, and it tailors the oil change to that schedule and predicts, on an ongoing basis, the oil life remaining so that that specific individual can plan an oil change accordingly. No other system can do this that effectively.

One thing is that I know personally from years of testing and thousands of oil analysis that the oil life algorithm works. There is simply no argument to the contrary. If you don't believe me, fine, but, trust me, it works. It is accurate because it has been calibrated for each specific engine it is installed on and there is considerable testing and validation of the oil life monitor on that specific application. NOt something that oil companies or Amsoil do. They generalize....the oil life monitor is very specific for that application.

Oil condition sensors in some BMW and Mercedes products are useful, also. They have their limitations, though, as they can be blind to some contaminates and can, themselves, be contaminated by certain markers or constituents of certain engine oils. Oil condition sensors can only react to the specific oil at that moment and they add complexity, cost and another potential item to fail. One other beauty of the GM oil life monitor is that it is all software and does not add any mechanical complexity, mass, wiring or potential failure mechanism.

There is considerable safety factor in the GM oil life monitor. Typically, I would say, there is a 2:1 safety factor in the slope of the ZDDP depletion curve....in other words, zero percent oil life per the ZDDP depletion is not zero ZDDP but twice the concentration of ZDP considered critical for THAT engine to operate under all conditions reliably with no wear. This is always a subject of discussion as to just how low do you want the ZDDP to get before the oil is "worn out" if this is the deciding factor for oil life. We would tend to be on the conservative side. If the oil life is counting down on a slope that would recommend a 10K change interval then there is probably 20K oil life before the ZDDP is catostrophically depleted....not that you would want to go there...but reason why many people are successful in running those change intervals.

Please...NOT ALL ENGINES ARE THE SAME. The example above is an excellent practical justification of why you would want to add EOS and change the 15W40 Delvac in the muscle car at 3000 miles max and yet can run the Northstar to 12500 easily on conventional oil. You must treat each engine and situation differently and what applies to one does not retroactively apply to others. This is where Amsoil falls short in my book by proposing long change intervals in most everything if you use their oil. It just doesn't work that way. You can run the Amsoil to 12500 with no concerns whatsoever in the late model Northstar because even the oil life monitor tells you that for conventional oil off the shelf. Would I do that to the 502 in my 66 Chevelle...NO WAY. Amsoil says I can though. Wrong.


There are entire SAE papers written on the GM oil life monitor and one could write a book on it so it is hard to touch on all aspects of it in a single post. Hopefully we hit the high spots. Realize that a GREAT deal of time, work and energy went into developing the oil life monitor and it has received acclaim from engineering organizations, petroleum organizations, environmental groups all across the board. It is not some widget invented in a week and tacked onto the car.
That was an interesting read; was this your actual experience, or was it copied/pasted from another source?

It would account for the rapid percentage drop during the winter months when I typically have ultra low mileage, but 15–30 minutes warm-up idles. But it doesn't account for why my numbers would drop from 100% to 94% when the oil was only one week old; only ~30 miles on that fresh oil; 50–80° outside temps. (minimal run time); and normal, light driving (no racing, hauling, etc.).

And the claim that it is “all software” is somewhat misleading. They may not have added any new (hardware, firmware, mechanical, etc) to provide the feature, but rather found another use for the many already in use for other reasons.
 

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That was posted on bobistheoilguy.com back around 2005. I forget the mans name. He may not be around today. The last revision was for direct injection engines. It is still all software.
 
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