I have been searching the web for an answer, and you would not believe how many experts there are on the subject of “the difference between motorcycle oil and automotive oil”. This would normally be fine except that there seems to be two reigning theories. One is that there is no difference between them and are interchangeable and the other is that they are not the same and they are specific to their purpose.
Some argue that since the engine, transmission and wet clutch are all in the same housing and share the same oil that automotive specific oils are “too slippery” and will cause the clutch to slip. This makes sense to me since the clutch packs in automatic transmissions are similar to the clutch on a motorcycle. IMHO automatic transmission fluid is very different to engine oil.
On the other hand the other field of experts argue that wet clutches desire oil and that it does not make a difference which oil you use. On top of that there are many experimenters who have tested top quality automotive oils in their motorcycles and there were no ill effects. I should add that there is another set of people that have done the same experiment and got different results.
Can anybody give me some insight on this subject?
On another thread there was a discussion about what type of oil to put in a car and someone posted a link to a very interesting and informative article on engine oil. I thought I knew about oil before I read this article. A large amount of ignorance was fought. Unfortunately he was strangely silent on motorcycle oil.
There is no such thing as motorcycle oil, for the most part; motorcycle manufacturers refer to the same specs as car manufacturers. However, motorcycles don’t have catalytic converters or some other components found on cars that might be poisoned by some additives, so specialty motorcycle oil often contains additives not found in ordinary motor oil. Whether they do any good or not is debatable, but there is no question that plain motor oil will work fine in any motorcycle.
AE Hass is a plastic surgeon. There are dissenters. He leaves out all discussion of the hydrodynamic wedge that forms in a bearing journal and holds metal parts apart. As I mentioned once on a leading oil forum, I drink my Koolaid thin.
I’d always thought that it was because gears have different needs in terms of anti-wear agents and viscosity / HTHS than engines do, and car oils are made for engines alone, while motorcycle oils are made to try and satisfy both needs.
There are oil boards(google BITOG) where people argue this kind of thing ad nauseam, as well as Dr. Haas’ articles and their impact, etc… You can probably pretty easily get enough info there to make up your mind one way or the other.
I had this very conversation with the local independant repair shop owner. His wisdom was that motorcycle oil just costs twice as much. He said that he uses Castrol GTX, because it isn’t “friction modified” or “energy conserving”. These features cause wet clutches to slip.
Back when I was in tech school it was explained that, in a unitary engine and transmission, the carbon chains would be mechanically broken down when continually run between the gears. On the other hand, this was taught by people who were good mechanics and had probably never stepped foot inside a chemical engineering classroom.
I don’t know. The gearing may or may not be hard on oil. Beyond that, it seems that small engines can have more than their share of hot spots or blowby, where coking can occur and where heat can otherwise damage the oil or the additive package.
I worked a few years as a motorcycle mechanic. We never did any sort of testing, but I never saw a clutch slip because someone put the wrong oil in the crankcase. I suspect that the additives in motocycle oil are better made to address the issues that arise in a motorcycle engine. I’ve also heard that the carbon chains in synthetics tend to be of a more uniform length, that this helps prevent coking, and this means the oil lasts longer.
Bikes tend to run at higher revs, yet the oil has to lubricate the loads in the gearbox and deal with the clutch without slippage.You do not want the oil foaming, but these circumastances make it more likely.The oil also has a more important role in direct cooling.
In addition, bikes usually have higher compression, and often closer tolerances - this is a pretty differant situation than most cars.
I know my VT1100 Honda’s clutch works a little better when I use the Mobil 1 V-Twin oil. With their automotive blends, I would get a little ‘lurch’ when I fully let out the clutch, but with the V-Twin oil, I don’t. The V-Twin oil costs about twice as much, but being fully synthetic, I figure a once-a-year change is fine, so I break even on cost. Your bike may be different, but I like the difference I feel, so I pay the difference in price.