[Anthony]

B. GM Oil Life Monitors

I worked extensively with the GM Research oil chemists that developed the GM Oil Life Monitor and know for a fact that it doesn't change anything in the model for cars with synthetic oil from the factory.
I agree that it is possible, under certain conditions, to run the oil past 15,000 or even 20,000 miles in passenger cars with the oil not being "used up" or "worn out"...but...that is assuming no safety factor at all in the oil life and it is under the best of conditions. And...the testing that proved this was NOT synthetic. If the oil is being used under conditions that allow an extremely long change interval then conventional oil will last just as long as synthetic under those conditions.

The other thing to keep in mind with oil drain intervals is that different engines have distinctly different oil lifes. The life of the oil in the engine is VERY dependent on the engine design, features in the engine and what is expected of the oil. As an example from the engines that I work on, the 93-99 Northstar engine would have a maximum oil life of 7500 miles. This was bumped up to 12,500 miles with the redesign of the engine in 2000 model year. This is the maximum oil life under optimum operating conditions, not the recommended change interval all the time. The difference in the engines is that the 2000 engine has rolling element cam followers instead of direct acting lifters. The rubbing element or direct acting lifters take the anti-wear ZDP out of the oil much faster and the direct acting tappets are far more dependent on oil quality and the presence of the ZDP to live. Oil that would be depleted of ZDP in the earlier engines in 7500 miles is still serviceable at 12,500 miles in the newer engines.

Older passenger car engines had rubbing element lifters, rubbing element rocker arms, pushrod tips, distributor gears that drove the oil pump, spur gear oil pumps, etc... Those engines needed a lot of antiwear protection and used it up quickly. 3000 mile oil changes on those engines with the oils of the day were probably stretching it under some conditions. Modern engines have gerotor oil pumps, no distributor gears, rolling element everything in the valve gear....they do not chew up the oil nor need high levels of anti-wear additives. Plus, the improved PCV systems keep the oil cleaner.

Motorcycle engines, like the FJR, still have rubbing element, direct acting tappets that need lots of ZDP and take the ZDP out of the oil fairly quickly. Synthetic has no advantage nor makes any difference in this respect. In addition, the oil lubricates the gear box where the gear mesh shears down the oil viscosity and takes even more ZDP out of the oil. Wet clutch action contaminates the oil also and is another source of ZDP depletion.

Since the basic model for oil life involves the linear depletion of ZDP in the oil due to metal-to-metal contact at lifter interfaces, gear interfaces, etc. I would guess that a motorcycle engine degrades oil life much more rapidly than a car engine...probably twice as fast. Also, motorcycle engines turn twice the RPM of car engines for any given maneuver so that multiplies the oil degradation by 2. The oil life algorithms (that have proven to accurately model engine oil life beyond a shadow of a doubt) actually count engine revolutions to establish the basic oil decay rate...so...the more revolutions the greater the degradation. This linear decay rate is multiplied by various factors that account for the oil operating temperature, ambient conditions, soak times, run times, engine load and many others. Short trips in cold weather will add considerable deterioration because of the effects of contamination by gas and water. Since cold weather operation is not much of a factor with bikes and they do tend to get thoroughly warmed up each ride (most people don't "housewife" a bike on short trips and many stops) I would guess that the main factor in oil life with bikes is the depletion of the anti-wear additives....which would be the same with synthetics or conventional oil.

C. ZDP Facts

The thing that is always touchy about oil change intervals is just how low do you let the ZDP concentration get before you consider the oil used up..?? ZDP is sacrificial and must be present at the wear site to work, so....as the concentration depletes there is less and less ZDP and the available molecules of ZDP are spread out more and more and may not be where you want them to be. On a long trip, there is little worry about too hot of an operating temperature, or contamination by blowby (the oil is always warm) so the ZDP depletion is the issue. On the GM oil life monitor, if ZDP depletion is the only determining factor, we typically use a safety factor of around 2 for the maximum oil life. So....if the oil change interval would count out to 12,500 miles, the oil could really go 25,000 before the ZDP were COMPLETELY depleted. You really don't want to run that far or push the ZDP to zero but it is an example of the safety factor in the calculation so I am sure that Yamaha does accordingly. My logic here is that Yamaha is not publishing an oil change interval that would take into account only long trip riding like this so there must be additional allowance for that type of riding. Plus, I know that under that type of usage, where the ZDP depletion is the determining factor the change intervals I am familiar with (the 12,500 miles) still has considerable safety factor so I suspect that there is little risk with a good oil to running the FJR to 8K on a long trip.

ZDP is a compound with Zinc and Phospates in it. It is an excellent anti-wear additive. Trouble with ZDP and gasoline engines is that it takes out the catalytic converter. Any oil the engine burns passes the zinc and phophates into the exhaust and both will contaminate and poison the cat. So....the whole emission compliance of gasoline engines depends on the catalytic converter so protecting it is primary.. That is why ZDP is minimized in gasoline engine oils and the drive is to push the concentrations even lower. That is why modern gas engines have features that I mentioned (like roller followers, roller rocker arms, no spur gears, no distributor gears, etc..) that do not require much anti-wear protection (the hydro-dynamic bearing film formed by the oil is adequate for those devices) and thus do not deplete the anti-wear additives in the oil.

Want ZDP...???....go to a GM parts counter and buy a can of GM Engine Oil Supplement (EOS). It is straight 40 weight oil highly fortified with ZDP. EOS has about 10 times the ZDP of normal engine oil so it is an excellent additive to "spike" the oil with ZDP for breakin or to avoid further wear in a marginal lube situation. ZDP is expensive and has to be blended into the oil with heat so it isn't something that can just be eyedroppered into the oil. But you can use an oil that is high in ZDP (like EOS) to spike the oil in the crankcase. BTW...you don't get any ZDP in any of the aftermarket snakeoil additives.

Too much ZDP can also play havoc with wet clutches so there is a balance as to how much you want in the oil.

ZDP is, in effect, an "anti-flux" agent. Where a fluxing agent would clean and help a weld form.....ZDP "fouls" the weld that is the wear agent and prevents micro-welding and the resulting material transfer and scuffing and scoring. Point being that the ZDP MUST be there when any metal-to-metal contact occurs at a surface asperity that breaks thru the thickness of the oil film. If the oil film is thick enough then there is no metal-to-metal contact and the ZDP is not needed. So, the concentration of ZDP must be great enough to ensure that it is exactly where it is needed at the time it is needed.

Engines ran for decades back in the early 1900's on oil that was rated SA....so called "virgin" motor oil.....i.e..NO anti-wear additives what so ever. And the engines lived fine to some extent. Living proof that oil could run for long change intervals if ZDP depletion were the only issue. BTW...you can still buy this at the dollar store...read the can....SA rated...no additives....good for door hinges and keeping the dust down on the dirt road.

It just depends on how comfortable you are with the situation and what the chances are that the particular engine you have will "need" the anti-wear protection to live.

The only answer I have for you is a statistically oriented example. If you ran a large population of engines for 10,000 mile change intervals they would likely all make it fine. If you ran an identical group for 20,000 mile change intervals maybe 3 or 4% would fail. If you ran them for 30,000 mile change intervals, maybe 6 or 8 percent will fail. ETC.... You could NEVER change the oil for 100K and some of them would make it. Would this prove you never need to change the oil...??? People tend to look at ONE example of an engine running long change intervals and deduce that it is fine. NOT. As a manufacturer we look at millions of vehicles and engines and the statistical evidence of when the engines are going to need lubrication service to determine the change intervals, acceptable anti-wear limits and oil life monitor degradation factors. A lot of this is hard to argue with as it is extremely difficult to get enough statistical evidence to make a hard and fast recommendation...so...we tend to be very conservative. Is an engine likely to live thru 20K change intervals...probably... It might just be sqeeking by....but it might make it. Poor gamble in my book unless you have some VERY detailed and precise oil analysis basis and an oil life monitoring system to guage the operating conditions.

All this is why the issue of oil and change intervals and such is so interesting and always promotes a discussion. There is just no hard and fast rule to go by for all engines and all situations ....