My 93 850 (non-turbo) w/ 110K burns about 1 quart of oil every 1500-2000 miles. By the time I get to the 3000 mile oil change mark, it's almost 2 quarts low unless I add some in between. The car doesn't smoke and runs well, but it's driven on the highway at high speeds mostly which probably contributes to it. I notice that it burns more oil when I use 10w30 rather than a 40 weight. My question is, should I try running 20w50 or switch to synthetic oil like Mobile 1? I'm just trying to get it to go 3000 miles without having to add any.

This car (purchased when it had 79K on it) has always burned a little oil, is that common for 850's? My BMW with 155K on it doesn't burn a drop.