Originally posted by psfred
take an older engine run on dino oil with long oil change intervals and pull the valve cover.
this line right here invalidates the logic because oil changes should be performed every ~3000 miles.
REGARDLESS of what oil you use (dino or synthetic) oil changes should be scheduled frequently and regularly. if the oil changes had been done every 3000-4000 miles the engine should still look like new.
my 1987 2.3-16 has 90,000 miles on it (granted it's not a lot) and has seen all scheduled maintenance at the dealerships and oil changes every 3000 miles and there's NO trace of any sludge. furthermore, i only use conventional oil. no synthetics.
i'm not arguing the "detergent"-like properties of synthetic oils. i'm just stating that the comparison is flawed. synthetics are engineered to last longer than conventional oils and it's well known that conventional oils should be changed frequently.
if you're one of those lazy types when it comes to maintenance and routinely leave the oil in 5000 miles or more then you should use synthetics because they will maintain its ability to lubricate and protect engine components more than conventional oils at high mileage. but if you ARE changing your oil frequently then there's no point in using synthetics. not at 2x the cost.