Probably because, while synthetic oil like Mobile One was around in
1986, not many people were using it so there was no need to warn against
it. By 2000, synthetics became very popular and for some reason, they
don't want you to use them.
The reason is probably because they have no control over what synthetic
you use, and they are all different.

Are there SAE or equivalent standards for synthetics as there are
regular oils?

With dino oil, they are all very
similar and the only main difference (other than things like sulfur
content) is the additives.

In other words, all good dino oils meet the various industry
standards.

So they can do testing with a high quality
dino oil and be reasonably assured that the results are reproducable
with other high quality dino oils. But with synthetics, the base
formulas and properties can be very different. Just look at the
evolution of Mobile One and you'll see that it's formula changed
drastically several times from when it was introduced in 1973; 1992,
1996, 1999, and 2002.

I wonder why the formula changed "drastically" so many times? Were
there problems?

Others have mentioned how well synthetics work in their cars; but it
seems to me that comparison is flawed. My automotive 350, at 60 mph
and 20 mpg, burns three whole gallons per hour. My twin boat 350s, at
similar rpms are each burning twelve gph. The flame front/peak
pressures/wall temp inside each cylinder is much different than any
car engine. It isn't automatic that what works at 3 gph will still do
a good job at 12 gph (at WOT it is 22 gph per engine.)

www.mobil1.com/why/synth/history.jsp

Steve

On 2 Sep 2003 20:58:43 -0700, (Bob) wrote:

Probably because, while synthetic oil like Mobile One was around in
1986, not many people were using it so there was no need to warn against
it. By 2000, synthetics became very popular and for some reason, they
don't want you to use them.
The reason is probably because they have no control over what synthetic
you use, and they are all different.

Are there SAE or equivalent standards for synthetics as there are
regular oils?

Yes, the same ones. But meeting the standards doesn't tell an engine
manufacturer all it needs to know about how their engines will perform
with a particular oil. For instance, in the synthetics vs. the natural
oils decision, they all meet the same standards. But they definitely
don't perform the same in ways that the standards testing doesn't
measure.

With dino oil, they are all very
similar and the only main difference (other than things like sulfur
content) is the additives.

In other words, all good dino oils meet the various industry
standards.

Yup.

So they can do testing with a high quality
dino oil and be reasonably assured that the results are reproducable
with other high quality dino oils. But with synthetics, the base
formulas and properties can be very different. Just look at the
evolution of Mobile One and you'll see that it's formula changed
drastically several times from when it was introduced in 1973; 1992,
1996, 1999, and 2002.

I wonder why the formula changed "drastically" so many times? Were
there problems?

I'm sure the company would call them "improvements." Just like anything
else, more R&D leads to changes in the product. However, when you
change the product with synthetics, you are changing the base
constituents that make up the oil. When you change the product with
natural oils, you're mainly changing just the additive package. The
base oil hasn't changed much in a very long time.

Others have mentioned how well synthetics work in their cars; but it
seems to me that comparison is flawed. My automotive 350, at 60 mph
and 20 mpg, burns three whole gallons per hour. My twin boat 350s, at
similar rpms are each burning twelve gph. The flame front/peak
pressures/wall temp inside each cylinder is much different than any
car engine. It isn't automatic that what works at 3 gph will still do
a good job at 12 gph (at WOT it is 22 gph per engine.)

That's probably why the manufacturers would rather you stick with what
they know works. Even if something else might work better, to them it's
an unknown until they test it.

Steve