Don't know about aviation engines (although I can find out easily enough), but I do know what the big thing these days in marine engines is extended service intervals with synthetic oils. They are MUCH cheaper long term, and increase the time between overhauls to boot.

Please note that constant speed/constant load applications aren't what most engineers would consider severe use, unless someone grossly under-sized the engine and it runs at full throttle most or all of the time. I've heard of GM 350 diesels, surely one of the most unreliable diesel engines ever put into production since 1960, running for decades as driving pumps. Low load, always running.

Aircraft engines only see heavy service in takeoff or emergency conditions -- otherwise, they are running well below their maximum output ratings, and there may also be some regulations on oil changes, etc -- no one is going to use expensive oil if you have to change it on short intrevals and disassemble the engine at specified hourly intervals anyway, it's wasted money. That doesn't mean mineral base oils are better, just less expensive.

I get all the noise about cheaper being confused with higher performance I need at work. Price is never the sole consideration for anything -- leave that issue alone, please, and stick with the actual functional qualities of the oil, not the price on the bottle.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!