The below is what I learned the hard way, after suffering engine oil induced clutch slippage myself. It is not my intention to argue the point with anyone because I know the futility of that. I am relaying my bad experience because of poor engine oil choices that I made, and what I learned about engine oil labeling standards that make choosing an automotive engine oil that is safe for wet clutch operation more difficult than I had realized. If this helps anyone that is good. If it doesn't, I wasted fifteen minutes of my time and one cup of coffee.
Being 10W40 or heavier weight is no assurance that the oil is safe for wet clutch use. Neither is it not being labeled as resource or energy conserving.
Because of this, in my opinion, there are two options if one is concerned about using an oil that will not harm their wet clutch.
One option is to purchase an engine oil that claims that it is suitable for use in wet clutch operation. There are many oils that state this. Usually the label will state something to the effect of
meets the requirements of JASO MA. The decision that needs to be made with this choice is whether or not you trust whoever is responsible for what is written on that label, and that when they state that it
meets the requirements of, that this claim is based as much in truth as it is in marketing.
Note the use of the terminology that usually is something to the effect of
meets the requirements of ...... It is written this way because it has never been submitted for certification, so it has never been proven to meet that specification. As such, it can not be labeled that it does without being sued by JASO. Without certification, it is then up to you to believe it or not.
The other option is to purchase engine oil that is certified by JASO as a JASO MA oil. Note the use of the terminology again. It will state that it is certified JASO MA, and will have a JASO MA certification mark and certification number on it. JASO MA certification is the best, and the only verifiable assurance, that an oil meets the wet clutch specification.
The label can state that it meets whatever standard that they want to write on it. Without JASO certification, anything else is hope, wish, or conjecture that has not been certified.
The above is what I learned after suffering clutch slippage myself. I had never used engine oils that stated Resource Conserving, Energy Conserving or Energy Conserving II on the label. I used the same oils for many, many years up to that point. I wasn't sure why I began having clutch slippage when I never had before. After some research, I discovered that engine oil standards had changed. More importantly, so had the labeling standards. I found out that automobile engine oil is allowed to contain, and may very well contain, much of the same friction modifiers in it as Resource Conserving, Energy Conserving or Energy Conserving II oils do. But because this oil does not meet the full registration requirement of the resource or energy conserving specification, it is not labeled as such. Now you have an oil that can be harmful to a wet clutch without any way of knowing this. This is in fact why the Japanese motorcycle manufacturers launched the JASO MA certification in the first place, because the lack of Resource Conserving, Energy Conserving or Energy Conserving II being on the label no longer meant that the oil was safe for wet clutch use.
I switched to a JASO MA certified engine oil, and after flushing out the harmful additives, my clutch slippage went away.
In addition, as far back as 2017 API was supposed to cease licensing the use of the Energy Conserving and Energy Conserving II labeling for any oil service classes below SN. This means that all of the oils that are rated SL or SM that previously had Energy Conserving and Energy Conserving II listed on the label still have those additives that are harmful to wet clutches, but they may no longer state Energy Conserving and Energy Conserving II on the label to let you know this. This is why to this day, or least the last time that I checked, Honda continues to call for SJ rated engine oil.
I am not a chemical engineer who keeps up to date with what the lubrication industry is doing. Nor do I follow what changes the certification authorities make to the labeling that may or may not affect wet clutch operation in a motorcycle when that oil was not intended for motorcycle use to begin with. It is more effort than I am willing to put in to choosing an engine oil. My research told me that I was causing my clutch slippage problem by thinking that I was smarter than the motorcycle manufacturers by using non JASO MA certified engine oil to save a few bucks. Once I realized that I wasn't, I decided that to much effort is required to keep up with all of the changes that are always happening, and that one needs to be aware of to make an intelligent choice.
Now, I just buy JASO MA certified oil and go ride.
A word of thanks to LEE (
@beemerphile), a member of this forum.
Most, if not all, of what I learned about oil certification, labeling, and why JASO MA is the best assurance available because of changes to oils and labeling standards, and why my choice was harming my clutch and why I was able to stop it before any permanent damage occurred, is because of the vast knowledge of Lee, and his willingness to share that knowledge with me and educate me. He no longer seems to post on this forum, which is a shame and a loss for this forum. His knowledge is helpful.