I found this on another forum!


In the United States, "synthetic" oil is a marketing gimmick.

Around 10 years ago, Castol started using hydrocracked group III in their "full synthetic" oil. Mobil sued them and lost. So now group III is allowed to be labeled full synthetic. Most major brands selling full synthetic, including Mobil 1, are in reality group III oils (highly refined dyno oil) blended with either or both group IV and group V base stocks. (group IV and group V are true synthetic molecules) The exception are the very high priced synthetic oils from companies like Redline, Maxima and Motul (specifically 300V) Those oils are the real deal. It's also why they cost $15 a quart. No oil for $5 a quart is really 100% synthetic. It's just economics.

Motul 5100 is labeled semi-synthetic because it uses group III blended with group V (ester). That's because it's a European based company, and the laws are different there. In Europe, to be called full synth, the oil needs to actually be all group IV or V. However, Motul 5100 'semi synth' is just as synthetic as Mobil One or many other "full synth" oils sold in the US. Motul calls it semi, because it's not 100% ester like 300V.

But actually a high quality group 3 blended with ester comes very close to a true full synth. Unless you're racing and banging it off the rev limiter for hours at a time, Motul 5100 is plenty good enough lubrication. Also Motul has patented additives to aid in positive gearbox actuation. It's why so many people report their bike shifts so nicely with it.

Nobody should feel bad or "ripped off" because Motul 5100 is "only" semi-synthetic. Most other brands in the US advertised as "full" synthetic are in reality no better than Motul 5100. They are group IIIs blended with PAO (group IV) or esters (group V), just like 5100.

As an anecdote, I don't think any other brand uses as high of an ester % in their blends as Motul. 5100 has a strong fruit smell. Stronger than some other expensive oils full synth, that are mostly PAO with a splash of ester.
In terms of cost, ester is the most expensive synthetic to manufacture, more than PAO. Both cost more to make than group III highly refined dyno.
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My rotary days taught me basically the same thing: most "full synthetic" oils are just synthetic blends.

I was under the impression that a true 100% synthetic oil has only a single viscosity (50 as opposed to 10w50). Any truth to this?

So is it safe to assume the KTM reccomended Motorex is a real full synthetic? I do pay $19/qt. It better be a real full synthetic...

But...is Motorex actually fully synthetic.??? Just want it clear...

I just found this from another forum!!

My local bike shop, run by a friend, let me sit in on a visit from the Motorex rep recently. The 15/50 oil - labelled as synthetic but actually a semi was developed primarily for the mille.

The non synthetic component was included to stop clutch slip but in all other respects is a full synthetic.

Been using it for last 1000 miles with no problems.

In reading my owners manual...it say to use Motorex power synt 4t which is fully synthetic...
I wonder about warantee if not using fully synthetic oil..???
Further reading says you void your warantee doing your own oil change under warantee period..
I got the extended warantee..Hmmmm...guess I won't worry until it ends..

When I was a chemist, I made a purely synthetic oil. It remained a liquid at -70C and would not boil in a full vacuum at over 300C. It cost about $100K (1989 dollars) per quart though. Oh well, nothing's perfect.

I have used the Motul 5100 on a few bykes and found it to work quite well. One problem with the fear of synthetic blends is that you really dont know if there is one drop per fifty five gallons of crude or a percentage closing in on fifty. It really is a crap shoot. I do not see why a person liking Motul products, who has a motorcycle that calls for full sythetic oil changes would not just move into the 7100 line, meeting the 4T full synth requirements.
Truly it can not be price.