Most motorcycle manufacturers recommends motorcycle-specific oil, pointing out that car motor oils have been reformulated and no longer meet the needs of motorcycle engines. Oddly enough, they usually make no distinction between the use of synthetic or petroleum-based oils even though it's an established fact that synthetic oils are a better lubricant. Full synthetic oils offer truly significant advantages, due to their superior high temperature oxidation resistance, high film strength, very low tendency to form deposits, stable viscosity base, and low temperature flow characteristics as compared to traditional petroleum-based oils. Yada, yada, yada ...
They also make no distinction between petroleum and synthetic oil when recommending oil change schedules even though the oil manufacturers suggest that synthetics can be run two-to-three times the mileage of petroleum oils between changes. The oil drain interval that is specified in the owner's manual is for what is called normal service. Normal service is defined as the engine being at normal operating temperature, at highway speeds, and in a dust-free environment. Stop and go, city riding, trips of less than ten miles, or extreme heat or cold puts the oil change interval into the severe service category, which has a shorter recommended change interval. So, manufacturers are saying to change your oil even more often anyway because no motorcycle experiences only normal service conditions.
Consequently, longer drain intervals should not be used to balance out the higher cost of the synthetics. Synthetic oil can be considered cost-effective only if the potentially higher rebuild and repair costs associated with increased engine wear are factored in. There is no convincing evidence, so far, that synthetic oils lowers these costs in motorcycle engines.
According to their manufacturers, motorcycle-specific oils are claimed to be formulated with additives that reduce engine wear. Specifically, they point to the use of zinc dialkyldithiophosphate (ZDDP) as the prime anti-wear additive used in all engine oils. ZDDP, however, contains phosphorous that has a life-shortening effect on the catalysts used in exhaust emission equipment, first only on cars, but now more recently on motorcycles. So the Environmental Protection Agency mandated a reduction (from a maximum of 0.12% down to 0.10%) of anti-wear additives containing phosphorous in automobile-specific engine oils.
It's important to note that this reduction was only required for the "energy conserving" lower oil viscosities of 0W-20 through 10W-30. The thicker oils were not required to meet this lowered phosphorus level. That is not to say that oil manufacturers won't lower the ZDDP levels in their 40 and 50 weight viscosity oils in the future. Since additives cost the oil companies money, if they feel that they can get by with less, they probably will be inclined to do so. Also, standardizing the additive packages across all viscosities would also simplify their production process. It's important to note here that, formulating oil with higher levels of anti-wear compounds than is needed, simply results in unnecessary combustion chamber deposits. Which is why most oil companies LOWERED anti-wear compound levels even before EPA required it.
So far however, tests have shown that automobile-specific Mobil 1 15W-50 (a viscosity exempted from the mandated reduction) has had no change in phosphorous level in its formulation. Further, Motorcycle Consumer News tests have shown that after the EPA-mandated reduction, Mobil 1 motorcycle-specific oil has now only about 15% more phosphorus than automobile-specific Mobil 1 15W-50 and about 6% more zinc.
Keep in mind however that, even though automobile oils now contain somewhat lower levels of ZDDP, Exxon-Mobil still states that Mobil 1 automobile oils "exceed the most-demanding protection requirements of modern, high-reving, powerful 4-stroke automobile engines ... yada, yada, yada." So, where's the reason to believe that the lubrication requirements of street motorcycles is measurably different? It seems clear that the current anti-wear additive levels in modern synthetics (both automotive and motorcycle blends) provide greater protection than required in any high performance motorcycle engine during the suggested oil change interval.
The oil manufacturer's advertising that directly equates reduction in engine wear with the tiny percent changes of ZDDP in the oil is misleading the consumer at best. It's well known that majority of engine wear is known to more likely occur during the metal-to-metal contact of a cold start, an operating condition best handled by a synthetic oil's very high film strength properties. Increasing the amount of ZDDP in the oil does no good if there's no oil coating there at startup.
Catalytic Converter Models
The latest models are now being shipped equipped with catalytic converters. Since motorcycle-specific oils with higher levels of phosphorus are now verboten by EPA for use in these models, I'm curious what oil the bike makers will now recommend? Maybe automobile-specific Mobil 1 15W-50.
Exxon-Mobil claims, as a selling point, that the formulation of motorcycle-specific Mobil 1 MX4T has none (?) of the oil additives called friction modifiers (usually molybdenum-based but not necessarily) that could lead to clutch slippage in some wet-clutch motorcycles. This is not an concern, of course, for dry clutch models. But, this IS supposed to be the current compelling reason to avoid some automobile-specific formulations of Mobil 1 that now contain friction modifiers to meet fuel economy mandates, when previously they did not. At it turns out, wet-clutch slippage can be a problem, and seen more often when you use the lower viscosity 10W-30 Mobil 1 and other oils that are designated "Energy-Conserving" on the bottle. As a perspective on this issue, a Oct 2000 Motorcycle Consumer News test showed that the molybdenum content of Mobil 1 MX4T motorcycle-specific oil is 5 ppm and 11 ppm for Mobil 1 15W-50 automobile-specific oil.
Combine a lower viscosity oil with a formulation that includes additional quantities of molybdenum-based friction modifiers and you get the Energy-Conserving designation in the API Service label on the back of the container.
But, automobile-specific 15W-50 Mobil 1 doesn't carry this designation ... because of its higher viscosity. A higher viscosity oil's resistance to flow is the reason why automobile-specific oils that are not energy conserving have been used successfully in wet-clutch motorcycles without slippage problems. So 15W-50 Mobil 1 works fine in wet clutches. Keep in mind however, that because motor oils loose 30% (or more) of their viscosity in the first 1,500 miles, you will tend toward wet-clutch slippage later if you prolong your oil change interval.
A frequent marketing claim made for motorcycle-specific oils is that they retain their viscosity longer than automotive oils when used in a motorcycle. That is, 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.
Nevertheless, when tested by MCN, the best-performing oil of the group tested was Mobil 1 automotive oil. Based on their test results, here's their advice:
1. Use a synthetic oil. The viscosity of synthetic-based oils generally drops more slowly than that of petroleum-based oils in the same application. There is no evidence that motorcycle-specific synthetics out-perform their automotive counterparts in viscosity retention when used in a motorcycle.
2. Change your oil more frequently, and more often than 3,000 mile intervals that is normal for cars. Motorcycles are somewhat harder on an oil's viscosity retention properties than cars. (The gears in the transmission are probably the significant factor in cutting the longer oil molecules into shorter pieces that are less viscous.)
3. Use the Mobil 1 in the 15W-50 viscosity only. The recent reformulation of thinner viscosity versions of Mobil 1 make them inappropriate for both wet and dry clutch applications.
Better Detergent Additives
Exxon-Mobil claims, also as a selling point, that Mobil 1 MX4T is specifically designed for sport bike needs and therefore uses a different dispersant/detergent technology for "better high-temperature performance and engine cleanliness." Without an explanation of this technology it's hard to be specific here but one thing is certain. Water-cooled motorcycles operate at similar temperatures as cars do so this presents no obvious advantage here. The dispersant/detergent issue is probably more directed at wet-clutch designs where abrasive friction material particles are suspended in the engine lubricating oil, so there's no distinct advantage to dry-clutch motorcycles. Changing your oil frequently negates this issue.
Separating the oil manufacturers' marketing hype from fact is difficult for the consumer. Given that the role of marketing is to enhance their oil's image and persuade you to switch to it, be sceptical when presented with unsupported claims.
A tactic often taken is: more is better. In this case, if the higher levels of anti-wear compounds advertised in motorcycle specific oils are good, still more is better, right? Maybe, but using oil with higher levels of anti-wear compounds - than needed - will cause increased combustion chamber deposits. That is why most oil companies LOWERED anti-wear levels before the government mandates intended to protect catalytic converters.
Another approach, enhancing their product's status through premium pricing and sponsorships (that are essentially paid endorsements) are effective ways of positioning their product to convince you, the consumer, that you're getting the very best when you buy it.
If you're not a product engineer, guidance from sources like Consumer Reports can be useful here in making informed decisions. For example, they did a quality comparison of several products a few years back and found that the less expensive products often worked the best and had the highest quality, but noted that people tended to buy the more expensive products because they thought they would be better.
Keep in mind that your dealer's will first recommend what they sell, and it's natural to expect that they'll try to sell products with the highest profit margin, all other things being equal.
The bottom line here is, to get the best protection, you need to change any oil frequently. Changing your oil serves to remove abrasive dust ingested from the air, from (wet) clutch wear and harmful combustion by-products from the engine that accelerate wear. Studies have shown that most motor oils loose 30% of their viscosity in the first 1,500 miles.
So for the best motorcycle engine protection, dry clutch or wet clutch, I recommend (and use) the less expensive 15W-50 weight (remember ONLY 15W-50) automobile-specific Mobil 1 and change it every 1,500 to 2,000 miles.