I'm not sure what you mean but particles in the oil could affect tolerance by wearing down parts but I don't think that the type of oil would be a factor in this case. Other than synth's ability to suspend particles better of course. I really don't see how oil can affect tolerance but hey you're the boss so...

I'll look into the origins of this myth but I'm sure it'll end up being the usual situation. People don't know the answer or they don't understand something so they make stuff up. If the same stupid therory is repeated enough times,it becomes the rule. Just like how people believed the world was flat. Some ass was asked what the shape of the world was and instead of admitting he didn't know,he made something up. Simple.

My own half assed opinion on why you can't swap back would be that because synth is a better lube and bonds to parts better,maybe it masks bearing probs. So when you switch back to the inferior dino oil,you get failures and/or elevated engine noise as the synth is "washed" away. Or just simply,you get used to synth's superior properties; engine runs cooler,less noise,etc,then you put dino in and your motor is noisier,runs hotter,etc.

Several people with shit-tons of knowledge that I would consider trustworthy have told me it is not true.

I can think of potential arguments to go in both directions that would make sense, but I have no idea.

Whether or not it USED to be true and now isn't, I'm not sure.

based on what ive heard, 10w-40 was 10w-40 whether synth or dino, that was the main reason i never understood why it was believed you cant switch back.

it would seem that the thickness of the coating on the parts would only matter at start up, when the engine is "dry" because a thicker coat would decrease initial wear maybe-but if you can have a thinner coat on the parts yet still have the same friction coefficient, then it shouldnt matter i think. but thats off on a tangent-

anyway pertaining to the question-could it be that early synths had additives that reacted to the additives in the dino oil that destroyed seals? actually that dont make sense because then it shouldnt be compatible at all, dino to synth wouldnt be possible either.

just throwin stuff out there. i think it could possibly even be that some ppl took their vehicles to the dealer, took a chance and tryed synth-and didnt notice a difference that was worth the extra money. instead of switching back and saving money, they were told they couldnt switch back. cars come with synth now (most do i believe) so you have no choice but to use the more expensive synth. no more $15 oil changes. just another idea....

obviously u can switch back and forth with no problem according to the oil companies, so who the hell started this myth lol

Who knows? Like I said people make shit up! Btw I used to work for Ashland and one of my best friends works for Mobile and last I knew,because of manufacturing costs and price competition,the profit margin on synth isn't any better than dino,so the oil companys don't care which you use,as long as you keep changing it every 3000 miles!$$$$$$$$$

yea-i typed my post as u posted

Happens to me all the time! my left hand was crushed/cut in half in an accident,so I can't type worth a fuck anymore!

btw I almost forgot,when synth oil first came out we used to market it as a "bargain" based on the fact that you could go "twice as long in between oil changes". The funny thing is that most "experts" agree that there isn't any reason to not go 5000 miles between oil changes with dino,so excusing the higher price of synth based on a 6000 mile lof was marketing genius!!!

My buddy showed me a study where they ran a car for 100,000 miles,changing only the filter and topping off every 10,000. Drained the oil and found that it had only lost 11% of it's original viscosity. He also claims that you can run Mobile1 for 3000 miles,drain it,filter it,replace the additive package and put it right back into your bike 3 or 4 times before you'd have to replace it.:idk:

Found the reason why this was started. Old seal tech use to leak when you switched from one to the other, but if you have a newer bike you have nothing to worry about. If you have an older bike, it would be advisable to watch for leaky seals and oil comsumption.

Repsol 4T Sintetico FTMFW. Smoother shifts than with KawiChem or Golden Spectro semi synthetics.

Thats what I use in the Zuk.

I use Honda HP4S full syn. I used Honda mineral for awhile, but I like the way the shifting feels with the full syn. Shifting stays silky smooth for the entire life of my oil. I change my more frequently than is needed though.