This may sound dumb, but... What exactly do they do? I tried searching for info but couldnt really find anything, so if anyone has a link or just could give me some in depth info that would be great. What could cause them to need to be replaced? Would running a lighter weight oil in a turbocharged engine have any effect on it? I ask this b/c mine need to be replaced (compression check showed that they did) and the previos owner was using 5w30 or something like that. Also what would happen if I were to drive the car for a while without replacing them as long as I watched the oil level?