Surprising New Evidence on the
|This article is from the February, 1994
Motorcycle Consumer News in the article "Motorcycle Oils vs. Automotive Oils".
Full credit for this article and study go to the original authors.
The detailed study that went into this article bring
up many valid points over the costs of motorcycle specific oils. Here at the Motorcycle
Performance Guide, we tend to believe the validity of the science used in the study, but
we still use high quality, synthetic oil in our race bike. Our street bike does not take
the level of abuse that the race bike does, so we feel the choice of oil is not quite as
Walk into any motorcycle dealership parts department
and you are virtually guaranteed to see prominent displays of oils produced specifically
for use in motorcycle engines. Since dealers are not about to waste valuable floor or
counter space on a product unless it produces a decent profit, it is obvious that
motorcycle-specific oils have become one of the premier parts department cash cows of the
Of course advances in lubrication technology have resulted in some fairly expensive
premium, synthetic and synthetic-blend products for automobiles also. But as you can see
from our pricing research at a half-dozen auto parts and cycle parts stores, the average
purchase price for the motorcycle-specific lubricants runs about 120 percent higher for
petroleum products and 185 percent higher for synthetic products than do their automotive
counterparts. (See Figure 1)
The companies marketing these high-priced motorcycle lubricants would have us believe that
their products are so superior to the automotive oils as to justify paying two and three
times the price. But are we really getting the added protection promised when we purchase
these products? MCN decided to look beyond the advertising-hype, specifically to see if
the claims of prolonged and superior viscosity retention could be verified. What we found
may very well change your mind about what should go into your motorcycle's crankcase in
So The Story Goes ...
Many motorcyclists have long doubted the need to pay the
inflated prices asked for most motorcycle-specific engine oils. An even larger number of
us have harbored at least some degree of skepticism about the claims made for motorcycle
oils, but have been reluctant to turn away from them, for fear of damaging our precious
machines if the claims should happen to be true. Most of this fear comes from very
successful marketing campaigns mounted by the manufacturers and distributors of
For example, a monthly trade publication for motorcycle dealers recently published an
article suggesting, "negative selling techniques" to "educate
customers" against purchasing automotive oil for their bikes. The example in the
article begins with the benevolent dealer looking the poor, dumb customer in the eye and
asking, in an incredulous voice, "You're not really using that in your motorcycle,
The idea, of course, is not so much to educate as to frighten the customer into paying for
the more expensive motorcycle oil that only guess-who sells. Such techniques have played
on our fears with great effect, to the point where high-priced, motorcycle-specific
lubricants have become staple profit producing items in the majority of motorcycle
dealership parts departments throughout the country.
The campaigns promoting motorcycle-specific oils have successfully indoctrinated an entire
Generation of motorcycle riders and mechanics. The doctrine is now so ingrained in the
industry that questioning its veracity instantly marks you as an ill-educated outsider.
Even MCN has fallen victim to the hype, espousing the superiority of such products in
these very pages. Our own technical experts from the American Motorcycle Institute have
repeatedly advised our readers against the dangers of straying from the straight and
What we, as well as the AMI, your local mechanic and all the other motorcycling
publications have been doing is simply repeating what we have been carefully taught to
believe over the years. The only problem with this approach is that our only source of
information has been the people who stand to profit from our faith in the superiority of
Stretching the Truth - Just a Bit
Motorcycle oil producers make a multitude of claims for their
products, some of which are extremely difficult to substantiate, and others which are
simply outdated and no longer applicable. This is not to say that all claims made for the
superiority of motorcycle oils are necessarily false, only that the actual differences
between them and their automotive counterparts may be considerably less than we have been
lead to believe. For example:
Claim - Since the introduction of catalytic converters in
automobiles, the best anti-wear agents have been limited by law to the amount that can be
used in automotive oils. but are present in greater concentration in motorcycle oils.
Fact - Phosphorous deteriorates the catalyst in converters
and is therefore restricted to a very small percentage in automotive oils. Phosphorous is
also an essential element in one of the best anti-wear agents, ZDDP (zinc
dialkyldithiophosphate), which is a primary component of such over-the-counter engine
additives as STP Engine Treatment.
While it is true that slightly increased concentrations of
ZDDP are found in some motorcycle oils (such as Spectro products), it is also true that
these concentrations still fall under the governmental limits, otherwise these oils could
not be used in the new converter-equipped motorcycles from BMW and Yamaha. Also, it should
be noted that ZDDP is a "last line of defense"-type additive, generally only
coming into play under extremely severe conditions where actual metal-to-metal contact
occurs within an engine, something that should never happen under normal operating
Claim - Motorcycle engines run hotter and rev higher than
automobile engines, therefore requiring oils with more expensive, shear-stable polymers
and additives than automotive oils.
Fact - This is one of those statements that was much more
true in the 1970s than in the 1990s. The big, slow-revving Detroit automobile engines of
the past have mostly been replaced with smaller, higher-revving four-cylinder and
six-cylinder engines that have much more in common with their counterparts running on two
wheels. Keeping pace with the development of the small, high-revving, automobile engine,
automotive oils have improved considerably, to the point where the newer, SG-rated
automotive oils are nearly identical to motorcycle oils.
In most cases where motorcycle oil producers show comparisons
between their products and automotive oils, you will find them using SE- or SF-rated oils
as the "automotive standard." These are oils that were designed and rated for
the cars of 10 to 20 years ago. We have yet to see a motorcycle oil compared in testing to
the 1990's standard, SG-rated premium automotive oils.
The Viscosity-Retention Claim
By far the loudest and most-believed claim made for
motorcycle oils is that they retain their viscosity longer than automotive oils when used
in a motorcycle. The standard claim made in most advertising is that motorcycle-specific
oils contain large amounts of expensive, shear-stable polymers that better resist the
punishment put on the oil by the motorcycle's transmission, thus retaining their viscosity
longer and better than automotive oils would under the same conditions.
This quote comes directly from the back of a bottle of Spectro 4 motorcycle oil, and is
similar to the advertising line used by nearly all motorcycle oils: Because of its special
polymers, Spectro 4 maintains its viscosity, whereas the shearing action of motorcycle
gears quickly reduces the viscosity of automotive oils.
We've all heard it a thousand times before. Our transmissions are the culprits that force
us to buy special, $6-a-quart motorcycle oil instead of the 99 cent special at Pep Boys.
We hate to have to do it, but we all know that it's true--or is it?
The question begged an answer, so MCN went looking for evidence that motorcycle oils
really are more shear-stable than their automotive counterparts.
Help From the Scientific Quarter
About the same time we began looking into the oil viscosity
retention question, we received a letter from John Woolum. a professor of physics at
California State University - and a motorcyclist - who noted that he was investigating in
the same area on his own. Not being ones to look a gift horse in the mouth, we contacted
Dr. Woolum and encouraged him to expand his research on our behalf.
Later in this article Dr. Woolum explains the laboratory procedures he used to generate
the statistics used in this article. but for the mean-time let's just take a look at the
bottom line when five popular oils (three automotive and two motorcycle) were compared for
relative viscosity retention after use in the same motorcycle. (See Figure 2)
As can be seen from the figures, the best-performing oil of the group tested was Mobil 1
automotive oil, a fully synthetic product. In today's market, virtually all oils sold are
to some extent para-synthetic, since even standard petroleum products usually contain at
least some synthetic-derived additives. However, for the sake of simplicity in this
article we have listed the products as petroleum if the primary components are from basic
petroleum stock. Those listed as synthetics have their primary components derived from
basic synthetic stocks, and may or may not contain any additives derived from petroleum
The results of these tests seem to support some of the
long-standing theories about oils while casting serious doubt on others. Going by these
tests it would seem logical to assume that:
1.The viscosity of synthetic-based oils generally drops more
slowly than that of petroleum-based oils in the same application.
2.Comparing these figures to viscosity retention for the same
oils when used in an automobile (see later text by Prof. Woolum) would indicate that
motorcycles are indeed harder on oils than cars.
3.The fastest and most significant drop in the viscosity of
petroleum-based oils used in motorcycles occurs during the first 800 miles (or less) of
All of these results (1-3) agree with everything the oil companies have been telling us
all along. However, the same test data also indicates that:
4.The viscosity of petroleum-based oils, whether designed for
auto or motorcycle application, drop at approximately the same rate when used in a
5.There is no evidence that motorcycle-specific oils
out-perform their automotive counterparts in viscosity retention when used in a
These last two results (4-5) definitely do not agree with
what the motorcycle oil producers have been telling us. In fact the test results not only
indicate the two motorcycle oils being outperformed in viscosity retention by the two
automotive synthetic products. but even by the relatively inexpensive Castrol GTX, which
is a petroleum product. This directly contradicts the advertising claims made by the
motorcycle oil producers.
The Oil Companies Reply
At Spectro Oils we talked to three different company
spokesmen, all of whom were helpful and provided us with a great deal of information about
their products. Unfortunately, despite our repeated requests for the testing data on which
their advertising claims were based, the 15 pages of "Lubrication Data" they
supplied us contained nothing that could not be found in their regular advertising and
marketing packages. No verifiable testing data has been forthcoming.
The Spectro spokesmen were not pleased when informed of our test results, but when
pressed, none could come up with a valid reason why their product should have scored the
lowest, either. The only comment we got was, "We only wish you had tested our Golden
Spectro synthetic instead of the petroleum-based Spectro 4."
Undoubtedly the Golden Spectro would have outscored the regular Spectro in our tests,
though how well in comparison to the Mobil 1 and Castrol products we can only guess at
When asked why the Spectro 4 petroleum product sold for $5.00 a quart when comparable
automotive oils could be found at less than $1.50 a quart, a Spectro spokesman insisted
theirs was "a superior, premium petroleum product, with expensive, shear-stable
additives that should outperform automotive oils." That being the case, it should
have been the perfect product for our testing.
We made a half-dozen calls to several different divisions within American Honda, but could
find no one willing to make any statement regarding their HP4 motorcycle oil. All of the
Honda employees we reached were friendly, and tried to help as much as they could, but you
must keep in mind that Honda is a huge conglomerate and sometimes the person with the
right answers to a question is difficult to track down through the corporate maze. Their
Accessories Product Management Division noted that they had a lubrication expert that
might be able to help us, but also that he was out of the country on vacation for the next
month and could not be reached before this article went to press. Should someone from
Honda wish to comment at a later date, we will certainly make room in a later issue.
Spokesmen at both Mobil and Castrol were a bit surprised at our questions, since neither
makes any claims for their products in a motorcycling context. However, when we explained
the test results, neither company spokesman seemed the least bit surprised, both noting
that automotive oils in general had made a quantum leap in viscosity retention technology
in the past five or six years. Both companies claimed to be using the very latest in
shear-stable polymers for viscosity retention, and while claiming no knowledge of the
motorcycle-specific oils' formula, expressed serious doubt that they could contain some
type of additive that was superior in this context to that already being used in their
automotive oils. Our test results support their assertion.
As we noted earlier, the viscosity-retention figures reported
in the table were the result of a series of tests conducted by Dr. John C. Woolum,
Professor of Physics at California State University. Since the validity of these tests is
likely to be called into question by motorcycle oil marketers, following are Dr. Woolum's
lab notes and explanations of the procedures he followed.
Relative Viscosity Retention Comparisons Among Five Brands
of Automotive and Motorcycle Oils
by John C. Woolum/ Ph.D.
Professor of Physics
California State University, Los Angeles
The central dogma of motorcycle oil manufacturers and
distributors has always been that motorcycles put different demands on their lubricants
than do automobiles. In particular, they point to the facts that motorcycles run at higher
temperatures and use the same oil in their transmissions as in their engines. The
transmission gears supposedly put extreme pressures on the oil molecules, thus causing the
long oil polymers to break down. High temperatures can have the same basic effect, as well
as additional effects such as the increase in oxidation products.
When the size of the oil polymers decreases ("cut up by the transmission gears,"
as at least one manufacturer claims), the oil thins. In other words, its viscosity
decreases, as well as its ability to lubricate properly. For example, what started out as
a 40-weight oil could effectively become a 30-weight oil, or even a 20-weight, after
prolonged use. What this means, effectively, is that if the claims of the motorcycle oil
producers are valid, they can easily be verified through measurement of viscosity changes
on various oils as they are used in different applications.
Measuring the viscosity drop in oils did not seem like too difficult a task, especially
since measuring viscosity of solutions of large molecules is a common practice in many
biophysics laboratories - mine included. My lab had all the correct equipment - in fact
the viscometers that I normally used for solutions of DNA and proteins were originally
designed for oil measurements.
Setting the Stage
Viscosity is a measure of the friction between two layers of
a liquid sliding relative to one another. It is usually measured in poise, or grams per
centimeter per second (g/cm. sec). The basic principle of many viscometers is to measure
the time required for a known amount of a liquid to pass through a capillary tube under
gravitational force. The time taken will depend on the viscosity and the density of the
liquid. The more viscous or less dense the liquid. the longer the time it will take to
flow through the capillary.
Therefore in reality, this kind of viscometer does not measure viscosity directly, but
rather the ratio of the viscosity to the density of the liquid being tested. This ratio is
called the kinematic viscosity. and the common unit for expressing it is in stokes or
The viscometer used for my measurements was an Ostwald-type, Cannon-Fenske 200, designed
to measure kinematic viscosity in the range of 10 to 100 centistokes (a centistoke is
one-hundredth of a stoke). The oils being measured had kinematic viscosity between about
10 and 25 centistokes.
For the test samples, I decided to use two types of oils designed specifically for
motorcycles and three types of fairly standard automotive oil.
The automotive oils were Castrol GTX 10W40 (petroleum based, $1.24/qt.), Castrol Syntec
10W40 (synthetic, $3.99/qt.) and Mobil 1 15W50 (synthetic, $3.48/qt.). The motorcycle oils
were Spectro 4 10W40 (petroleum based, $4.99/qt.) and Honda HP4 10W40 (petroleum/synthetic
Each of these oils was run in the same motorcycles 1984 Honda V65 Sabre-under as near to
identical conditions as possible. The oils were sampled for testing at 0, 800 and 1500
As temperature has a strong effect on viscosity, I had to make certain it was carefully
controlled for the experiments. Using a laboratory temperature control chamber, all
measurements were made at 99 degrees Celsius (error factor of plus or minus 0.5 degrees),
which is about 210 degrees Fahrenheit. This is the most common temperature used for oil
viscosity measurements. It usually took about 15 minutes for each sample to achieve
equilibrium within the chamber.
Each oil's kinematic viscosity was compared with its own kinematic viscosity at 0 miles to
establish the viscosity ratio. In addition, measurements were made of each oil's density
at each state of the tests. The densities were found to change by less than one percent,
which is about the limit of the accuracy of the measurements. Therefore, a ratio of the
times taken for the oils to pass through the viscometer effectively gives the ratio of
their actual viscosity, since the densities cancel out.
What this all means in layman's terms then, is that the ratio established for each oil at
the end of each test is a percentage of the amount of original viscosity retained at that
point. For example. the Castol GTX sample at 800 miles showed a relative viscosity of
0.722, meaning it had retained 72.2 percent of its original viscosity. Or, if you want to
look at it the other way, the Castrol had lost 27.8 percent of its viscosity after 800
miles of use in the motorcycle.
Just for comparison sake, I also tested the viscosity drop of the Castrol GTX automotive
oil after use in a 1987 Honda Accord automobile. At 3600 miles of use, the Castrol GTX
showed a relative viscosity of 91.8 percent.
As the Mobil 1 had retained so much of its viscosity after the 1500 mile test, it was the
only oil I allowed to run longer in the motorcycle. After 2500 miles, the Mobil 1 recorded
a relative viscosity of 79.1 percent.
Also, it is worthy of note that from a testing standpoint, the two most similar oils were
the Castrol GTX automotive oil and the Spectro 4 motorcycle oil. By similar, I mean that
they tested as having almost the same absolute kinematic viscosity and density right out
of the container. So starting out as equals, the Castrol maintained its viscosity several
percentage points higher than the Spectro, under the same use in the same motorcycle yet
the Spectro costs about four times the price of the Castrol.
The Error Factor
As a scientist, I must always ask myself. Are there possible
errors in these measurements that would make them invalid? One possibility here would be
that there was more particulate matter (contaminants) in some oil samples than in others,
which would increase the viscosity numbers of that oil. Particulates disrupt the
streamline flow and so increase the viscosity. (Einstein was the first to derive the
quantitive expression for the increase in viscosity due to spherically, shaped particles.)
Large particulates should have been removed by the oil filter, and a new filter was used
for each test. Still, to determine the effect of smaller particulates the oil samples were
centrifuged at 11,000 g (11,000 times the acceleration of gravity) for a period of 10
minutes. A considerable amount of particulate matter was found and removed in all of the
800 mile and 1500 mile samples. However, the change in viscosity made by eliminating these
particulates was found to be negligible.
Another possible source of error would be that the conditions to which the oils were
subjected were different. In all cases, the distances were comprised of approximately 70
percent city riding and 30 percent freeway riding. The range of temperatures and the
average ambient temperature during which the motorcycle was ridden were approximately the
same. If anything, the average ambient temperature was higher during the operation of the
motorcycle with the Mobil 1 oil, which should have put it at a disadvantage, yet it scored
the highest overall in the viscosity retention tests.
Of course the motorcycle did age somewhat during the testing period, which took place over
a year-long span. It registered about 4000 miles at the beginning of these tests and about
14,000 at the end. The order in which the oils were tested was: 1) Castrol, 2) Spectro, 3)
Mobil and 4) Honda.
The motorcycle oil producers have suggested that other
criteria. such as the amount of wear metals and contaminants, might be unacceptable when
using automotive oil in a motorcycle. To test this theory, I sent a sample of the Castrol
GTX at 1500 miles to SpectroTech. Inc., for a complete oil analysis. Their findings were
that all contaminants (water, dirt, coolant and sludge) were normal.
SpectroTech also reported that all wear elements (antimony, titanium, silver, copper,
lead, tin, aluminum, nickel, chromium, cadmium, sodium and boron) were normal except for
iron, which was reported as "mildly above normal" at 51 parts per million.
SpectroTech lists acceptable levels for all of the above listed metals except iron, for
which they state, "values vary greatly with systems and parts." so it is not
clear what exactly is meant by "mildly above normal." Perhaps it was in
comparison to cars with 1500 miles on the oil. Also, this could have been due to cam wear,
since the early Honda V-4s were known for excessive cam and rocker arm wear.
In any case, again I could find nothing to support the argument that automotive oils were
somehow less effective than motorcycle-specific lubricants when used in a motorcycle.
It could appear from this data, then, that there is no
validity to the constantly-used argument that motorcycle-specific oils provide superior
lubrication to automotive oils when used in a motorcycle. If the viscosity drop is the
only criterion, then there is certainly no reason to spend the extra money on oil
specifically designed for motorcycles. There does, however, appear to be a legitimate
argument for using synthetic and synthetic-blend oils over the petroleum based products.
In speaking to a number of people involved in the production,
marketing and distribution of motorcycle-specific oils, we could not find anyone who could
present a valid argument for discrediting the testing done by Dr. Woolum. In general, they
all tried to turn the conversation another direction by bringing up other possible
advantages to using their products, while ignoring the viscosity-retention question. Yet
without exception it is their own advertising that consistently brings the subject up,
touting the special shear-stable polymers as the primary reason motorcyclists should
purchase their products.
It is this practice to which we take exception, as we have been unable to find evidence to
support these claims. In short, it seems to be nothing more than a clever marketing ploy
designed to enhance their products' image and separate motorcyclists from their money.
MCN is ready to print any research or test results provided by the oil companies to
support their claims of superior viscosity retention, with this one proviso: The
comparisons must be against actual, SG-rated oil products that can be purchased off the
shelf at the average auto parts store. Tests against generic, basic-stock mineral oil or
against the lower-rated SE and SF oils would lack any credibility in a real-world context.
Despite more than six months of research, reading all the claims and counter-claims
printed by dozens of industry experts and lubrication experts, MCN cannot and does not
purport to know all there is to know about the differences between automotive and
motorcycle oils. However, what we do know is that we can find no substantive evidence that
using a high-quality, name-brand automotive oil in an average street motorcycle is in any
way harmful or less effective in providing proper lubrication and protection than using
the more expensive, motorcycle-specific oils.
Petroleum Based, Multiple Viscosity, SG-Rated, Oils
Best Retail Prices Found
Maxum 4 Premium
Average Price Differential: 319.5%
Synthetic Based and Petroleum/Synthetic Blend
Multiple Viscosity, SG-Rated Oils
Best Retail Prices Found
Golden Spectro 4
Maxum 4 Extra
Pep Boys Synthetic
Average Price Differential: 185.0%
|Relative Viscosity Retention
(as a percentage of
initial viscosity retained
after normal use in the same motorcycle)