Long time lurker here and couldn't find the info I need, so I decided to join. Excellent forum and information here. I have a 1992 BMW 325is with around 150,000kms that I just recently finished turbocharging and have been debating what oil to use for quite some time now. I've used GC 0w-30 for the past 15 months or so in the car and it seems to be working fine, but I'm not sure how it will hold up with the additional temperatures from the turbo. At bimmerforums.com, everyone seems to think that 100% GC will not provide enough protection, and most suggest I go with a mix of M1 0w-40 and 15w-50. Although that may work, I want to use GC if possible. I need suggestions on either what oil to run, if 100% GC is more than good enough for my application or if I should mix some CS 5w-50 in with the GC? Any suggestions are appreciated. Thanks.