George inMinneapolis wrote:
I have been using 20-50 Castrol auto motor oil in my R80/7. I read that Oak says you have to use Golden Spectrum, and I have heard it said that motorcycle oil should be used.
What's the difference between auto oil and motorcycle oil?
Part of the reason this is so confusing is because what was true years ago is not true today, so wise and correct advice from then is no longer as true. "Motor Oil" used to vary far less between automotive and motorcycle products. Then the EPA made emission laws, and cars started using catalytic converters. The EPA discovered that as an engine burned tiny amounts of oil, the anti-wear additives in the oil damage the catalytic converters. So, the last few "upgrades" of the API Service Categories (SF, SG, SJ, SM, etc.), have had ever stricter restrictions limiting those ingredients. I believe SG was the last spec before they started restricting those ingredients. These are the ingredients that are important for the solid lifter/cam-lobe interface. New autos have been designed to operate well with this newer oil, but our old motorcycles (and some old cars like VW's, Porsches, and some solid lifter Detroit engines) really need those ingredients, and were designed to run oil that contains them.
So, the auto oil made in the 70's and 80's was not very different from the motorcycle oil of the same period, but now there is a real difference.
Some riders switched to diesel oil when they started restricting the anti-wear additives in auto oil. Shell Rotella was a favorite: very reasonably priced, and all the old amounts of anti-wear additives. BUT, now they are starting to put catalytic converters on diesels, so the EPA has put additive restrictions on the latest diesel oil specs. So that strategy isn't as useful now as it was for the last 10 or 15 years.
Another issue with the new oils is the "energy-conserving" label. This oil usually contains "friction modifiers" which are lovely ingredients which make the oil even more slippery. Unfortunately, such oil can be problem for motorcycles with wet clutches. BMW's, until the F bikes came out, all had dry clutches, so, while this issue can be really important for most motorcycles, it's not an issue for these BMW's. The Japanese have set an oil standard for oils that are safe for wet clutches: JASO T904-MA and MA2.
George inMinneapolis wrote:So, any real problem using auto oil? Any big advantage to Golden Spectrum or other motorcycle oil.
G
Anti-wear components are used up as needed, so changing your oil more frequently is one strategy if running the newest automotive oils. A motorcycle specific synthetic oil has two advantages: synths can handle more heat before they break down, and they have substantially more of those anti-wear additives. Both issues become much more important the longer you run between oil changes. So if you change your oil every couple thousand miles, it's likely that it's safe to run whatever automotive oil you want. The longer you run between changes, and the hotter it is where you ride, the more likely that a good motorcycle specific synthetic can make a real difference in how long your engine lasts.
Edit: Also, any motor oil that is rated SF/SG still has those older levels of anti-wear ingredients, I believe some of the specialty companies (like Amsoil, Spectro, Redline, Royal Purple, etc.) are still producing automotive motor oils which are made to the SF/SG standards. Those oils have all the ingredients you need, and are much harder to argue against compared to "motorcycle specific" oils.
A further complication is that now many new motorcycles have catalytic converters, so who knows if the EPA will make new restrictions on motorcycle specific oil.
