I'm wondering what happens to the oil that is burned in a well-tuned catalyst-equipped engine. Does is deposit on the exhaust valves, the exhaust manifolds, cat converters, etc. or is it blown out into the air? Also, what exactly deposits? I'd imagine primarily the HCs would deposit as coke or whatever, but I've also read that the Phos (from the ZDDP) may deposit and foul the cats. This is why the EPA is concerned with Phos levels in oils. This question is not just academic, but really a practical one since my almost new 2001 Trooper burns a decent amount of oil. Vehicle has approx. 28,000 miles on it right now. It burns approx. one quart in 6000 miles. The engine is a 3.5 liter gasoline engine with a published 215 HP rating. Engine runs perfectly. It recently passed a NJ state dynomometer emmissions test. I'm concerned that as the miles roll on and the oil burns through, that the burnt oil may have negative impact on the engine's performance and the engine's emmissions. It burns approx. one quart in 6000 miles. I've read lots of stories (both here at BITOG, and elsewhere) about other late-model Troopers burning more significant amounts. Current oil is Mobil 1 0W-40. Are synthetics better or worse than dinos as far as leaving deposits? How about comparing regular dinos to high-additive dinos like the 15W-40 HD oils? I'm thinking that I (or rather my car's engine) would be better off with maybe a regular Pennzoil or some other regular dino rather that the PAO from Mobil 1.