Hey there gearheads and bimmer dreamers, I need to get some ground truth on a motor oil issue. After the last DIY ay Curry's I was speaking with one of their mechanic's and he was telling me about a Mobil 1 0W-40 motor oil recommended for bimmer engines that would free up a few horse power and increase gas mileage. I went for my last oil change at the Curry's Falls Church location and switched to the 0W-40 and over night my gas mileage went from around 450 miles a tank to around 550 plus miles a tank. I've done the basic proformance modifications such as CAI, Shark Injector and SuperSprint exhaust but the engine oil change has done the most in feul efficiency. However I was talking with my friend Mike Robinson at Sports & Imports and he was telling me that zero weight motor oil can cause leaks in high mileage engines. I just trying to run this to ground and find out if this is indeed a concern. I'm just over 227,500 on my 00 323i engine. Thanks in advance. Happy Motoring...