Back in my younger days I rode dirt bikes competitively (and now I am
paying for that physically!) running "Enduros" and other long-distance
(500 + mi.) rugged races. I rode in the open class (500cc or larger.)
Anyway, I started using synthetic oil (I mixed my own, disabled the oil
injection system) and had nothing but excellent results. One thing all
of us had problems with was fouled plugs -for a number of reasons
related to the kind of running we did. Synthetic oil simply stopped
that problem. I also noticed that the engine ran cooler overall (not a
giant difference, I was using high-quality Dino-oil to begin with) but
more importantly I didn't have ANY scoring on the cylinder walls after
making the switch. Previously it was fairly common after a long, hard
race to observe some scoring on the cyl. walls and pitting on the
piston top. We did a tear-down after every race so it was easy to see
the difference.

As for the quality of synthetics under heat/pressure in high stress
points like tappets or cams, I have been told that's not true. I don't
know... I can only go by what I personally observe and my engines are
as tight as they were when I bought them. If synthetic failed under
high pressure as you suggested, then it seems to me that many people
who use synthetic oils exclusively (like me) would have failures (or
unusual wear) particular to those parts, however that doesn't seem to
be the case.

Jeff



Gene Kearns wrote:
On 6 Jun 2006 11:31:59 -0700, "Chehalis Jeff"
wrote:

I have used synthetic oils exclusively in everything from my outboard
(synth 2-stroke) to my Volvo (300,000+miles) to my Dodge Cummins Diesel
(290,000+mi) and finally my Honda mini van (187,000+mi) all with
original engines - none of them burn oil and all have near-original
compression.

The ONLY problem with using a synthetic in an older engine is that
between the oil's detergent/cleaning capabilities and slightly lower
viscosity, if the engine is prone to leak oil, it will. I figure if my
engine leaks oil, I need to fix the leak and I don't mind if the
crankcase gets cleaner.

With synthetic oil, ALL my engines and transmissions

I have had excellent service out of synthetic oils, too. The only
disaster I have seen directly attributable to synthetics is their use
in high performance air cooled engines. Under high temperatures, the
oil loses it's EP properties and fails at high pressure points like
cam and tappets. Recip. aircraft oils are now either straight dino oil
or a synthetic/dino mix.

Interestingly, I wanted to use synthetics in my Suzuki outboards and
was advised by the manufacturer not to do so. When I questioned this
surprising position I was told that they couldn't recommend synthetics
merely because they were untested by the manufacturer.