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.
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.
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 catalytic converters 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.
Catalytic Converter Models
The latest touring models are now being shipped equipped with catalytic converters, and phosphorus is bad for these. Since motorcycle-specific oils have higher levels of phosphorus, is it now bad to use motorcycle specific oil in motorcycles?
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 that could lead to clutch slippage in wet-clutch motorcycles. 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.
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.
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:
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.
This is what I use M1 15W-50 (silver cap):
From their website:
Mobil 1 15W-50 is recommended for high performance vehicles including turbocharged and supercharged engines where a thicker oil film is desired. Its high viscosity provides outstanding performance in high-revving, high-temperature conditions.
Mobil 1 15W-50 fully synthetic motor oil exceeds warranty requirements for gasoline engines where an API certified oil is specified. It meets:
Requirements for Diesel Powered Vehicles where an API CF or API CD is recommended
Provides extra anti-wear additive for older vehicles
Mobil 1 15W-50 motor oil is formulated with SuperSyn, an extra-high viscosity synthetic fluid, plus extra anti-wear additive to provide extra protection for severe service applications such as towing, hauling and racing.
Mobil 1 15W-50 is also recommended for older valve train designs that may benefit from a higher level of anti-wear normally not required for newer generation vehicles. Mobil 1 15W-50 will also provide better anti-wear protection for higher valve spring tensions in certain racing engines.