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GM Cadillac OIL monitor algorithm - alghorythm

Old 03-13-2007, 01:27 AM
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Default GM Cadillac OIL monitor algorithm - alghorythm

i will not try to re-write this, it is best for you and anyone else to interpret it as you will.
i hope this answers all your questions. it is a long response, but a fairly complete one.

btw, the gent mentioned there below (***** & ****) are names well known in the Cadillac circles
and by the members of the old ACA - Allante Appreciation Group. i wil just leave it at that in
respect of the old days and protect the identity of the gent.

to "elaborate", no?


alghorythm / algorithm:

"Many computer programs deal with a substantial amount of data. In such applications, it is important to organize data in appropriate structures to make it easier or faster to process the data. In computer programming, the development of an algorithm and the choice of appropriate data structures are closely intertwined, and a decision regarding one often depends on knowledge of the other. Thus, the study of data structures in computer science usually goes hand in hand with the study of related algorithms. Commonly used elementary data structures include records, arrays, linked lists, stacks, queues, trees, and graphs."

Posted: Apr 19 2005, 08:34 PM
GM Oil Life Monitor
From *********

The GM engine oil life monitor counts engine revolutions and ac***ulates 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 ZDP 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 ZDP 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 ZDP 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 ZDP depletion curve....in other words, zero percent oil life per the ZDP depletion is not zero ZDP 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 ZDP 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 ZDP 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.



Oil Monitors Revisited

by Ed Newman
AMSOIL Marketing & Advertising Manager
This article appeared in National Oil & Lube News, February 2003

I just got this e-mail from a friend. It was his first oil change on a new 2003 Chevrolet Tahoe. He wondered how the vehicle could go so far without the oil monitor light going on.

He wrote, "I've never gone this far on an initial oil change before. Usually changed that oil out at 1500-2000 miles in the past. I had 5500 miles on the truck and it still had 23% of its life left in the oil." That calculates out to 7142 miles before it would have told him to change the oil, and 4.25 months (or 17 weeks) to reach the 7142 miles. He was curious about whether GM was lengthening the algorithm without telling consumers what they were doing.

Naturally I was curious to learn more and thought it a good opportunity to revisit an issue which five years ago seemed to put shudders into a lot of quick lube owners and operators. Did GM change the algorithm?

The matter came to his attention because the oil change light in his 2002 Chevrolet Tahoe came on much more often, even though it was the same engine, same drive train, and same travel route to work each day.

"Driving the same route, during spring and summer weather, my oil change light came on once at 3800 miles, and once at 4200 miles on my 2002 Tahoe. All things being equal, one would have thought that the severity of my driving during the colder months in the newer truck would have resulted in even shorter drain intervals as compared to my old one," he wrote.

I told him I'd be going to the SEMA Show in Las Vegas and would make it a point to find someone from GM who could address this issue. I also did some Internet research to see what else was out there.

A DejaNews word search on "oil monitor GM algorithm" yields a small number of search results. At the alt.autos.gm newsgroup, a writer notes that the "Oil Life System compensates for different driving styles and conditions.

The math model involves computerized monitoring of engine revolutions, operating temperature, coolant temperature, oil temperature, and other factors to calculate the rate of engine oil degradation and predict when it should be changed." It is an alternative to "fixed oil change schedules that may not be suitable for all situations."

As luck would have it, on my last day at the Specialty Equipment Manufacturers Association (SEMA) show in November, I was able to locate a representative from General Motors who could assist in clarifying some of these issues for us. For nearly half an hour I spoke with Al Cline, who works in the GM Powertrain, High Performance Vehicle Operations division. My speculation is that Mr. Cline knew more about these sensors than nearly anyone at the show.

By the end of the conversation he said I should fly to Detroit and talk with the woman who developed the GM oil sensor logarithm, Dr. Shirley Schwartz.

Here are highlights from my discussion with Mr. Cline.

1. The first cars with the oil sensor were the pushrod Cadillacs and Buicks in 1986, followed by the Alante. As noted above, the sensor does not actually assess oil quality. Instead, it uses an algorithm to model oil life.

2. Mr. Cline does not believe in oil change intervals without monitoring the driving style. He said that some people, based on the way they drive, should change oil every 2,000 miles, others 12,000. There are too many variables, he said, therefore the entire industry is skewed because there is no such thing as a routine oil change interval.

3. GM believes the algorithm monitor is the most accurate way to measure when oil should be changed. It is adjusted for each engine because engines operate differently.

One thing is clear from this discussion: General Motors has a different philosophy about oil change intervals than the oil industry. While oil companies rally round the 3,000-mile-oil-change-flag, the auto industry is marching to the beat of a different drum altogether.


Shirley E. Schwartz

outstanding contributions to lubrication
technology, development of environmentally friendly products,
conservation of non-renewable natural resources, and significant
achievements in promoting awareness of technical professions.

Developed a patented device that notifies a car’s driver
when the engine oil should be changed. Her area of expertise is the
conservation of engine oils for engines fueled with gasoline and
alternative fuels.

Old 03-22-2007, 03:30 AM
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Default RE: OIL monitor algorithm

from the same GM Eng above...

Just to set the record straight...the use of synthetic engine oil does nothing to increase the allowable change intervals. There are many reasons to change the oil. The oil oxidizes with temperature and time. The oil becomes contaminated with gasoline and water from blow by and combustion byproducts. The anti-wear additives in the oil becomes depleted. While the synthetic oils may not oxidze as quickly as conventional mineral oils they become contaminated just as fast and the anti-wear additives in synthetics deplete at the same rate. Nothing magic about synthetics that alllow them to remain in the crankcase any longer than conventional oils.

The myth of extended drain intervals was started by the oil companies in their attempt to sell the much more expensive synthetic products. For them to appear cost effective the idea of the extended drain intervals was created. Somehow the marketing guys at the oil companies conveniently 'forgot" about the fact that they had no more anti-wear additives (or the ZDP) than conventional oil.....

Somehow, the various engines and transmissions in the Allante were designed, developed and validated without the use of synthetic products.... They perform fine without synthetics.

I have nothing against synthetic oils and trans fluids....but...understand that the engines and trans were designed for conventional products and that the use of the synthetics is not required.

There is little or no benefit in using synthetics in either the engine or trans in normal driving. Period.

The oil life monitor does an excellent job of estimating the engine oil life. It takes all of the factors into account that cause the oil to need to be changed. It is the best guideline that there is for knowing when to change the oil as it tailors the change interval to the specific driving schedule that is being used. It is really impossible to tell someone exactly when they should change their oil as each persons driving schedule is different and changes constantly. That is why the oil life monitor is so handy....it tailers the oil change interval for each engine and each driving schedule.

Synthetic oil offers one magor advantage over conventional mineral oils....it can still function without serious degradation at oil temperatures above 300 degrees F. This is good...but....passenger car engines are designed and cooled so that the oil never gets that hot ...even under extreme conditions. If the oil never gets near 300...then what advantage is there in using an oil that its only advantage is that it can live over 300 degrees ?

Synthetic oil is the factory fill oil for several applications purely because it's high temperature capabilty allows the deletion of the oil cooler on the vehicle. Since the oil cooler is only required for the very few vehicles that get taken to the race track it is unnecessary cost , mass and complexity on most vehicles and creates a liability for leaks... If the synthetic is capable of protecting the few engines that go to a race track then it makes sense to use it instead of saddling every car in production with an oil cooler. The engine does not require it other wise. Neither does the trans.

I find it amazing that people change their trans fluid at 100K and find it necessary to put synthetic in. The trans made it 100K on the factory fill oil that was NOT synthetic...so what makes synthetic desireable now after 100K or more.?

A similar argument exists regarding the engine oil...

Old 03-22-2007, 03:58 AM
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Default RE: OIL monitor algorithm

again, same individual

much has been written about the coolant pellets. Search using GM coolant supplement or something like that. In any event, the Pellets are simply a sealer or stop leak if you like. There is nothing magic nor mysterious about them. They are simply ground up ginger root and walunt shells and are the same material that BarsLeaks puts in their sealer minus the dark soluable oil. The dry, powdered BarsLeaks "Gold" in the clear plastic tube at Walmart is the exact same material. The sealer or stop leak is recommended for the all aluminum engines due to the increased likelyhood of a tiny seep or leakage due to the difficulty in sealing aluminum at gasketed surfaces and the chance of porosity opening up in the diecast aluminum parts.

Almost every manufacturer of engines installs the cooling system sealer at the factory....Cadillac, Chevy, Gm, Ford, RollsRoyce....etc. The list of buyers that BarsLeaks ships to is long and distinguised. You can even buy the stuff at the Chevy parts counter as Chevies use it too....

The oil life monitor has been discussed many times also....in fact it was reviewed recently in a post just below....I think it is "leave well enough alone" if I'm not mistaken.

In any case the oil life monitor is a computer algorithm that models engine oil life taking into account all the things you mentioned as well as several others. The fundamental element of the algorithm is counting engine revolutions to establish a baseline curve of oil deterioration (depletion of the anti wear additives is purely a function of engine revolutions) and then adding severity factors to this based on coolant temp, run time, soak time, oil temp (for oil oxidation rate), etc..... The oil life monitor is very accurate at predicting actual oil life in the engine as it tailers the deterioration to the owners driving schedule exactly and takes into account any extreme situations (like an overheat or limphome or short trips or trailer towing...) and degrades the percent oil life left accordingly.

I would guess, based on what you said , that the oil was due to be changed due to short tripping the car, time since the last change and the oil is likely never getting to operating temperature due to the short trip driving. Many people don't realize that the worst possible thing to do to engine oil is to short trip the car. I've seen the oil life monitor "timeout" in as little as 500 miles in winter , short trip driving. The oil sampled from that test sequence had over 35% gasoline in it due to the fact that the engine had been started so many times and had never been warmed up ...!!! In winter driving like that you can actually see the oil level in the crankcase go UP as gasoline and water ac***ulate in the crank case. One long drive on the expressway to warm up the oil good will restore the oil and the oil life can/will compensate for this. On the other hand, repeated, long trip driving will often go 7500 miles on an oil change according to the oil life monitor. In any case, one year is the maximum I would ever recommend to wait for an oil change , especially in occasional use type cars.

The oil life monitor has undergone continuous development and retuning to suit the vehicle it is in and the engine combination. In addition, the improvement in the engine oils on the market is taken into account. In some cases, such as the Northstar, the engine has undergone design changes (roller followers for example-2000 MY) to allow longer change intervals as the oil is not depleted as quickly and is more tolerant of depleted oil... Today, the max change interval can go as high as 12500 miles on a Northstar (2003 model year) and is gong to be increased in the future to 15,000.

There is a lot of safety factor in the oil life monitor calculations for any given model year of car so there should be no concern in following the oil life monitor for change recommendations. In fact, as in your case, the oil life monitor was reset (apparently, it can't be reset to anything other than 100% and the message stayed away for 9 months!!) and it told you to change oil in only 1000 miles.....appropriate for YOUR driving style. That is the problem with giving an owner an oil change recommendation based purely on miles. I consider the 3000 mile change interval to be BS and a con perpetrated by the oil change and oil companies to sellmore oil....it is WAY too often for most drivers....but, in your case, it was not often enough. That is why it is best to follow the oil change indicator. It tailers the oil change recommendation to your specific driving and use habits.

The oil life monitor is on almost all GM cars these days and could save thousands of gallons of oil if it was followed by customers.....and probably prevent engine damage due to overlong changes in some cases.

Old 04-01-2007, 04:00 PM
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Default Cadillac RESET OIL CHANGE - monitor algorithm alghorythm

How is the Oil Life Indicator RESET?

Many GM cars:
- key in the on position, engine off,
- slowly press the accelerator to the floor 3 times
- watch the D.I.C. flash, 'Oil Life Reset'.

- hold in RANGE and AVG SPEED buttons for at least 5 seconds

CTS ..
PRESS "Info"
Scroll down and select "Engine Oil Life"...
Press "Reset".

any others? drop me a line ...

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