Originally Posted by Springerdad
Is that because of getting certification? Or is it oil additive formulaion? Curious.
Quite a few years back, Exxon introduced a full synthetic aviation grade oil. It was pulled from the market after a while, as it was discovered that full synthetic oil did not scavenge the lead (present in the fuel) adequately. So the lead gummed up valves, rings, etc. The lubrication properties were fine.
There are semi-synthetics in use now that work well and with the pending introduction of lead-free aviation fuel, we may see a re-introduction of full synthetics. I personally use Amsoil full synthetic in one of my airplanes that is certified for auto gas, but it's a liquid cooled Rotax engine that prefers a motorcycle-type oil.
Sorry for the thread drift.