Oil percentage - OLM information
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Northstar Engines and System Technical Discussion Discussion, Oil percentage - OLM information in Cadillac Engine Technical Discussion; hello everyone, I changed N*'s oil last week and have driven 223 miles, the oil % life left is on ...
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    eldoedwardo is offline Cadillac Owners Fanatic
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    Oil percentage - OLM information

    hello everyone,
    I changed N*'s oil last week and have driven 223 miles, the oil % life left is on 95. Is that because its so hot out, or using the air conditioner most of the time?Is the % equated by gallons used/miles driven/torque applied?
    The oil is top grade T5/w bosch filter ,my records indicate the % should be be around 97. Is this a big deal or normal?
    thanks Ed

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    Ranger's Avatar
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    Re: oil percents

    Oil life remaining is a calculation made by the PCM. It uses a LOT of different parameters in decrementing the oil life remaining, including miles driven, throttle position, ambient temperature, engine temperature just to name a few. It knows if you are making short trips in winter or highway driving in summer.

    Here's how it works. (written by a GM powertrain engineer)

    "One thing I can touch on and clear up.....the GM oil life monitor operation and my statement that ZDP (or ZDDP as you tend to call it here...most of the API literature just sticks to ZDP so I tend to use that) depletion is the basis for oil deterioration.

    My spelling is poor but ZDP stands for zinc dialkyldithiophosphate which , as it sounds, is an anti-wear compound comprised of zinc and phosphorus.

    ZDP is dispersed in the oil so as to be at a potential wear site if a surface asperity happens to break thru the oil film thickness causing the dreaded metal-to-metal contact. A molecule of ZDP must be present at that moment to prevent microwelding at the contact site which will cause material transfer, scuffing, scoring, wear and catostrophic failure. The concentration of ZDP in the oil will determine if there is ZDP present to work it's magic. The greater the concentration...the more likely a molecule of ZDP will be there...and vice versa.

    By nature, ZDP is sacrifical. As ZDP is "used up" at a wear site to prevent micorwelding the concentration of ZDP decreases.... So...if you measure the ZDP concentration in engine oil in a running engine it will decrease at linear rate based on engine revolutions. Any given engine has a certain number of high potential wear areas where metal-to-metal contact could occur due to reduced film thickness and/or surface asperities....areas such as rubbing element cam followers, distributor gears, rocker arm pivots, push rod tips, etc...... The more of these areas the more ZDP depletion. The more often these features come in contact the greater the ZDP depletion. That is why, generally speaking, ZDP concentration in the oil, for any given engine, will decrease at a fairly linear rate when plotted versus cummulative engine revolutions. The more times it turns the more contact the more chance for wear the greater the depletion. This is as much of a fact as I could quote ever and is really not speculation or anything. It is proven beyond a shadow of a doubt in many studies. That is why it is ONE of the basis for determining oil life remaining and why it is THE basic premis of the GM oil life algorithm. It is only ONE of the things that determines oil life...but it is the one thing that can be tied to engine operation in a linear fashion and estimated very accurately by accumulating engine revolutions via a counter.

    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 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."

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    Re: oil percents

    if you won't read the info Ranger has posted (i recommend you do) here's the short version

    oil life is tied to temperature and rpm (basically)

    the colder it is when the engine is started has a lot to do with it and the more times the engine turns over the faster the oil loses it's 'life'

    you could have idled for 10 hours and driven no miles but the oil life will still be going down
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    Holy crap that was an awesome read.

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    Re: Oil percentage - OLM information

    Quote Originally Posted by andyoww View Post
    Holy crap that was an awesome read.


    it's been posted and re-posted here over 50 times (just search for dialkyldithiophosphate​)
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    Re: Oil percentage - OLM information

    Very few people believe that an engine incurs less wear on a 1,200 mile highway trip that it would in two weeks of city commuting.

    Your OLM will drop less on that long trip than in the city driving situation.

    It's all (plus other vital Northstar info) up in the Cadillac Technical Archive - in the top ^^^ black bar.

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    Re: Oil percentage - OLM information

    Thanks Ranger, That was just the kind of info I was hoping for.Submariner I do believe you are correct. It seems others enjoyed it also.
    Chris you having a bad day? If you try ,you'll have a better one

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    Re: Oil percentage - OLM information

    not at all edloedwardo, i was just making sure anyone reading this thread gets the idea that this is not new info in any shape or form and if they want to search for that keyword they can find tons of valuable discussion on the subject

    i can see how that might have come off differently than I intended ... but you've got to add a tone of voice to it to accomplish that misinterpretation
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    Re: Oil percentage - OLM information

    Quote Originally Posted by eldoedwardo View Post
    Chris you having a bad day? If you try ,you'll have a better one
    Hah !! I came within a gnat's whisker of posting the identical "info". The sheer number of times this discussion has been repeated in here and in the Seville/Deville forums over the years is simply mind-numbing.

    ............. and the true, GM, technical, hands-on engine builder discussions in Cadillac Technical Archive (way up there ^^^) have been there since at least 02/06, my join date. That was the first few lines of links/tabs I read before I joined.............and the sticky posts at the top of each forum - they're full of necessary info.

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    Re: Oil percentage - OLM information

    trying to pronounce dialkyldithiophosphate is mind-numbing!

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    Re: Oil percentage - OLM information

    Of course, you could go with the antiquated, way outdated, more expensive, more time consuming, bigger pain in the but, but tried and true 3,000 mile oil change interval.

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    Re: Oil percentage - OLM information

    3,000 miles used to be forever.................

    Now you know what the Kendall Oil logo really stands for..............

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    Re: Oil percentage - OLM information

    We've come a long way
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    Re: Oil percentage - OLM information

    Yep ^^^^, and all 3 of these are now blended/bottled by SOPUS: Shell Oil Products US

    (Quaker State and Pennzoil are NOT refined from Pennsylvania crude any longer...............)

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    Re: Oil percentage - OLM information

    The info Ranger posted above is a good read, but to the best of my knowledge, GM has never confirmed how the OLM really calculates oil life remaining. The info posted above indicates that engine revolutions are the primary measure of the calculation for oil life. I've read elsewhere that fuel injector pulses are what is used. They are obviously related, but the strength (length) of the fuel injector pulse may provide a better indicator of how hard the engine is working than strictly revolutions. Despite the info in the article that he reposted about ZDDP, I've never seen this confirmed nor do the hundreds of used oil analysis samples I've seen support this theory. Most used oil analysis samples show about the same ZDDP as new out of the bottle. What the samples do show is a very good tracking of the acidic buildup of the oil. Most believe that when the oil's Total Base Number (TBN) is 1.0 (almost totally acidic), the oil is "done". Whether the OLM uses revolutions or fuel injector pulses (with degrades as mentioned in his article for oil temp, startups, etc), and whether it really calculates TBN or ZDDP degredation, I'm a firm believer in the OLM.

    I've been doing used oil analysis for years and feel the OLM tracks the oil's life very well. On the highway the OLM counts down at about 1% every 100 miles in my GM cars. In short driving, stop and go, it counts down much faster. In my CTS-V which only saw very short commutes, it counted down at about 1% every 40 miles or so, thus your drop of 5% over 200+ miles is very much in line with how fast my CTS-V OLM counted down.
    Here is an example of used oil analysis on my 06 CTS-V (now sold).
    Cadillac CTS-V Used Oil Analysis
    Notes:
    - June 07 sample was Mobil 1 5w30, the rest AMSOIL 0w30
    - The OLM was at 25% for the first three, 24% for the last one
    - Zinc and phosphorus remained at about their new in the bottle levels (API specs limit phosphorus to 800 ppm)
    - TBN tracked fairly well with 25% life remaining on the OLM
    - Wear metals (Aluminum, iron, copper, lead) decreased over the four samples showing a well wearing engine

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