Hi. I'm new to this site but I have tried searching for the answer with no luck. Is Mobil1 oil Group 3 or Group 4? I'm specifically talking about 15-50 and 0-40 that I stockpiled in the end of '06. I recently put 15-50 in my car, and then more recently put in Auto-Rx. Apparently ARX is fine with any oil in the clean phase but I just wanted to check if I should use it on the rinse phase. I'll most likely run dino oil but since I have this oil here, I was just wondering. Thanks!