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Old 03-24-2010, 11:34 AM   #1
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Join Date: Nov 2008
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GM's OLM & synthetic oils.

I'm stealing these two posts from chevymalibuforums, browsing through there this morning and thought if anyone is up for the read, there is some pretty interesting information on how GM developed it's OLM, and how it works; in addition to how that interacts with synthetic oil and extended drain intervals.

Here is a link to the thread, only so I don't feel like a thief-

I don't know the authenticity of this information or its sources, but it sounds pretty right to me. Here is about the OLM-

Originally Posted by Washboy
Re: GM Oil Life Monitor: Do you trust it?
From bbobynski on

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 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.

The oil life monitor is not under the control of a summer intern at GM Powertrain per an earlier post....LOL Not that a summer intern wasn't compiling calibrations or doing a project on it but is under control of the lube group with a variety of engineers directly responsible that have immediate responsibility for the different engine families and engine groups. The idea that a summer intern was responsible for or handling the oil life monitor is ludicrous.....LOL LOL LOL
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Old 03-24-2010, 11:37 AM   #2
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Join Date: Nov 2008
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Here is more about the OLM, in addition synthetics and extended drain intervals-

Originally Posted by impacted
Re: GM Oil Life Monitor: Do you trust it?
Here it is...

ere is another take from another website, probably the same fellow(

The following is the response of a GM engine development engineer to a
motorcycle forum on extended mileage oil changes. The link to the forum
was posted on VV months ago. I found it so interesting I saved a copy.
Read with an open mind and form your own opinion about your favorite oil
and oil change habits. Only the GM engineer's responses to questions,
converted to plain text format, are included. The GM engineers
experience and credentials are in the first few sentences of the last
paragraph. It's taken special handling to get this long message posted,
thanks to vv-help. I've got the entire original in pdf format for those

John Dozsa

Keep in mind that there are a lot of reasons to change the oil. Oil
oxidizes with time and temperature, oil gets contaminated with
combustion byproducts, oil gets contaminted with soot from blowby, oil
gets contaminated with fuel and water...particularily during cold
starts, acids form in the oil, oil gets contaminted with dust/dirt/
debris, the antiwear additive in the oil (the "zinc" or ZDP) gets
depleted with engine revolutions, the antioxidants/
anti-acids/detergents/dispesant additive deplete with time and engine

Synthetic oil addresses the oxidation as it will handle higher
temperatures but that is about the only advantage of
short, using synthetic does NOTHING to allow a longer drain interval.
Synthetic has the same amounts of ZDP, same problem with fuel and water
contamination, same problems with other contaminates including soot,
same problem with acid buildup, etc.... All reasons why synthetic oil
does NOT allow longer drain intervals. The water from combustion
byproducts/blowby combines with the sulfur in the fuel in blowby to form
sulfuric acid over time so oil acidity slowly increases with time and
miles and synthetic oil does nothing different to prevent this. You have
to change the oil before the anti-acids in the oil additive package are
overwhelmed. If oxidation were the only reason to change the oil then
synthetics would have an advantage in terms of life or extending the
drain intervals. Unfortunately, oxidation due to temperature is RARELY
the determining factor for the drain interval so any advantage
synthetics might have in this area are moot. I would recommend sticking
to the recommended drain intervals even if you use synthetic oil.

It is interesting that the new Mobil 1 "extended service" oils added
more ZDP to the oil to prevent depletion of the anti-wear additive to
market the extended drain intervals to 15,000. the bottle.
It specifically states that if your engine is under warranty, change the
oil at the specified much for their "guaranteed
15,000 mile interval. Another gem on the bottle is the statement that
"if your engine has an oil life monitor follow the oil life monitor and
do not use the extended drain interval." The bottle also says that the
extended service is void if the engine operates in heavy
duty/commercial/livery service, is idled a lot or is operated in a dusty
environment. That pretty much eliminates a LOT of other applications and
matches the manufacturer's recommendations for sooner oil changes under
those conditions. So..after reading the can, exactly what good is the
"extended service" Mobil 1. In addition, if youlook carefully, the
extended service Mobil 1 does not have the API SG3/SG4 rating as it
exceeds the antiwear (zinc) concentration for the API SG3/SG4 ratings.
This is not necessarily bad for motorcycles but makes the oil a
NON-recommended oil for most modern passenger car applications. I am not
making this the fine print on the bottle yourself. I would
change the oil at the normal intervals even if you do use a synthetic

It isn't MY is a fact. Mobil even says the same thing.
They have not stated anything about extended drain intervals with their
products until the recent addition of the "extended service -15000"
synthetic oil. And they had to modify their existing Mobil 1 product to
make that claim (modified to the extent that it doesn't conform to the
SG3/SG4 specs anymore) and they STILL put tons of qualifiers on the
15000 claim with the disclaimer about changing it according to the
manufacturer's oil life monitor, and changing it sooner if under
warranty or operating in towing/commercial service or dusty
environments. I am not making that the bottle for yourself.
With all the other reasons for changing the oil there is no way that
synthetic can claim a longer drain interval. I worked extensively with
the GM Research oil chemists that developed the GM Oil Life Monitor and
know for a fact that it doesn't change anything in the model for cars
with synthetic oil from the factory. I agree that it is possible, under
certain conditions, to run the oil past 15,000 or even 20,000 miles in
passenger cars with the oil not being "used up" or "worn
out"...but...that is assuming no safety factor at all in the oil life
and it is under the best of conditions. And...the testing that proved
this was NOT synthetic. If the oil is being used under conditions that
allow an extremely long change interval then conventional oil will last
just as long as synthetic under those conditions. The single advantage
of synthetic is it's ability to operate at temps above 305 F without
oxidizing rapidly. Since there are few applications where the oil gets
that hot the advantage is moot and contributes zero to extended drain
capability. Even my CBX with a partial fairing blocking part of the
engine never gets the oil to 300 even running on the freeway at 80 in
summer weather...I've checked. The fact is that the "extended service"
claim for the Mobil 1 15000 oil is a bit hollow...especially when they
add several $$$ per quart for the 15000 oil. A modern Cadillac Northstar
or LS1 engine will go 12500 miles on the oil life monitor if used in
highway driving, best case conditions...and that is validated with
conventional, non-synthetic oil !!! So for the extra $$$ for synthetic
and extra $$$ for 15000 you only get 2500 extra miles...and Mobil tells
you on the bottle NOT to ge 15000 if your car has an oil life monitor.
If you saw data showing the oil was fine with extended drain intervals
then conventional oil would have done the same thing on that particular
test. Forget the idea that synthetic allows longer drain intervals. It
is hype by some of the synthetic marketers (primarily Amsoil) to
sell/justify their expensive (highly profitable) product. They test
under one set of best case conditions and then imply that that is the
case for all conditions.

The other thing to keep in mind with oil drain intervals is that
different engines have distinctly different oil lifes. The life of the
oil in the engine is VERY dependent on the engine design, features in
the engine and what is expected of the oil. As an example from the
engines that I work on, the 93-99 Northstar engine would have a maximum
oil life of 7500 miles. This was bumped up to 12,500 miles with the
redesign of the engine in 2000 model year. This is the maximum oil life
under optimum operating conditions, not the recommended change interval
all the time. The difference in the engines is that the 2000 engine has
rolling element cam followers instead of direct acting lifters. The
rubbing element or direct acting lifters take the antiwear ZDP out of
the oil much faster and the direct acting tappets are far more dependent
on oil quality and the presence of the ZDP to live. Oil that would be
depleted of ZDP in the earlier engines in 7500 miles is still
serviceable at 12,500 miles in the newer engines. Older passenger car
engines had rubbing element lifters, rubbing element rocker arms,
pushrod tips, distributor gears that drove the oil pump, spur gear oil
pumps, etc... Those engines needed a lot of antiwear protection and used
it up quickly. 3000 mile oil changes on those engines with the oils of
the day were probably stretching it under some conditions. Modern
engines have gerotor oil pumps, no distributor gears, rolling element
everything in the valve gear....they do not chew up the oil nor need
high levels of anti-wear additives. Plus, the improved PCV systems keep
the oil cleaner. Any oil claims of extended drain intervals that do not
make the distinction of what type of service or what type of engine
should be highly suspect and considered primarily a marketing ploy.
Period. Motorcycle engines, like the FJR, still have rubbing element,
direct acting tappets that need lots of ZDP and take the ZDP out of the
oil fairly quickly. Synthetic has no advantage nor makes any difference
in this respect. In addition, the oil lubricates the gear box where the
gear mesh shears down the oil viscosity and takes even more ZDP out of
the oil. Wet clutch action contaminates the oil also and is another
source of ZDP depletion. Since the basic model for oil life involves the
linear depletion of ZDP in the oil due to metal-to-metal contact at
lifter interfaces, gear interfaces, etc. I would guess that a motorcycle
engine degrades oil life much more rapidly than a car engine...probably
twice as fast. Also, motorcycle engines turn twice the RPM of car
engines for any given maneuver so that multiplies the oil degradation by
2. The oil life algorithms (that have proven to accurately model engine
oil life beyond a shadow of a doubt) actually count engine revolutions
to establish the basic oil decay more revolutions the
greater the degradation. This linear decay rate is multiplied by various
factors that account for the oil operating temperature, ambient
conditions, soak times, run times, engine load and many others. Short
trips in cold weather will add considerable deterioration because of the
effects of contamination by gas and water. Since cold weather operation
is not much of a factor with bikes and they do tend to get thoroughly
warmed up each ride (most people don't "housewife" a bike on short trips
and many stops) I would guess that the main factor in oil life with
bikes is the depeletion of the antiwear additives....which would be the
same with synthetics or conventional oil. Understand, also, that any
modern oil that meets the SL or SM API performance requirements have
quite a bit of synthetic content in them. Any multivis oil that meets SM
performance specs must have a synthetic polymer Viscosity Improver
package or it wouldn't pass. So, any modern oil is a synthetic "blend"
as some companies like to market and charge extra for....LOL.
Amsoil.....?.....That is an oil marketing company that utilizes a
pyramid scheme to sell their product thru a system of distributors and
dealers and such. They know absolutely nothing more about oil than Mobil
or Texaco or the other major oil manufacturers. Their bogus claims are
meant to sell their products at high prices to benefit their pyramid
marketing scheme. How could they justify the high price they charge for
their product otherwise. Their products probably perform well to some
extent but they have no outstanding attributes that others do not have
for half the cost. Their claims of long change intervals are completely
nonsense. They base them on the lower oxidation rates of their synthetic
products at high operating temps. As mentioned, that is rarely, if ever,
the defining factor in oil changes and the testing that determines the
oxidation rates is run at temps above what most engines will ever
operate at. They take something completely out of context and pretend
that it is a big advantage. It isn't. If you look at all the tests that
oils must pass to meet the API standards for performance, Amsoil only
quotes selected results in areas of testing that do not replicate normal
engine operation. If you really understand ALL the things that govern
oil life Amsoil's claims evaporate. They make themselves sound very
technical and quote lots of "data" but it is a smokescreen to cover
their marketing scheme that benefits their distributors and dealers.....

First, though, let me be clear. Synthetics, such as Mibil 1, are
excellent products. They can survive at temperatures well above the
oxidation limits of conventional oil of 305 F. If an engine operates at
those oil temperatures then synthetic is applicable. Synthetic offers
good low temperature viscosity and pour points... low meaning below -40.
Down to the -30/-40 range conventional oils are fine. If you are
searching for oil on the northslope and cold start regularily at -40
then consider synthetic. Other than that, synthetic oil's usefulness is
questionable in passenger cars. Racing teams use synthetic oil for
several reasons. First and foremost is marketing. If it is "good for
racing" then it must be great stuff, right??? Fooled you , didn't
it..!!! LOL LOL The racing teams get paid lots of sponsorship $$$$ to
run the oils and put the stickers on the cars. That is why they use it.
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