The factory warning light does jack s***, it only turns on when there is no pressure (or no oil). An aftermarket gauge will show the pressure dropping as you loose oil, but in order to actually see that you have to either be watching it constantly or get one that has a programmable alarm. That turned out to be really annoying when I had the MS3, half the time I was watching the road, half the time I was watching my DH for detonation, temperatures and pressures.