|
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(vv.corvair.org/pipermail/virtualvairs/2005-July/028037.html)
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
interested.
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
revolutions.
Synthetic oil addresses the oxidation as it will handle higher
temperatures but that is about the only advantage of synthetic...so...in
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. BUT....read the bottle.
It specifically states that if your engine is under warranty, change the
oil at the specified intervals...hmmm....so 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 up....read the fine print on the bottle yourself. I would
change the oil at the normal intervals even if you do use a synthetic
oil.
It isn't MY conclusion...it 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 up....read 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 rate...so...the 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.
|