Home XS11 Info
Narrow screen resolution Wide screen resolution default color martini color standard color MNS color

Motorcycle Oils vs. Automotive Oils Print E-mail

Motorcycle Consumer News

February, 1994

Motorcycle Oils vs. Automotive Oils

Surprising New Evidence on the Viscosity-Retention Question

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 1990s.

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 the future.

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 motorcycle-specific lubricants.

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, are you?"

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 narrow path.

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 motorcycle-specific oils.

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 utomobiles, the best anti-wear agents have been limited by law to the amount that an 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 conditions.

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 products.

Preliminary Conclusions

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 use.
    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 viscosities of petroleum-based oils, whether designed for auto or motorcycle application, drop at approximately the same rate when used in a motorcycle.
  5. There is no evidence that motorcycle-specific oils out-perform their automotive counterparts in viscosity retention when used in a motorcycle.


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 this point.

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.




< <
Figure I
Petroleum Based, Multiple Viscosity, SG-Rated, Oils
Best Retail Prices Found

Motorcycle Oils

Name Price
Honda GN4
Kawasaki Premium
Maxum 4 Premium
Motul 3000
Spectro 4
Torco 4-Cycle
Torco MPZ
Average Price/qt. 3.80
Automotive Oils  
Name Price
Quaker State
AC Delco
Castrol GTX
Average Price/qt. 1.19
Average Price Differential: 319.5%
Synthetic Based and Petroleum/Synthetic Blend
Multiple Viscosity, SG-Rated Oils

Best Retail Prices Found

Motorcycle Oils

Name Price
Honda HP4
Golden Spectro 4
Maxum 4
Maxum 4 Extra
Motul 3100
Torco T4-R
Average Price/qt. 6.53
Automotive Oils  
Name Price
Castrol Syntec
Mobil 1
Valvoline Hi-Perf.
Valvoline Racing
Pep Boys Synthetic
Average Price/qt. 3.53
Average Price Differential: 185.0%


Figure II
Relative Viscosity Retention

(as a percentage of initial viscosity retained
after normal use in the same motorcycle)

  0 miles 800mi 1500mi
Mobil 1
Castrol Syntec
Castrol GTX
Honda HP4
Spectro 4

Donate to XS11.com

Enter Amount:

Login Form