I'm going to swim against the stream here. I had M1 SM 5w-20 in my Saturn (96 DOHC model, 125K) and drained it . MPG was 32-35MPG in my daily commute which is almost all highway miles at 65-70MPH. Performed a "poor man's flush" with PZ dino, then filled the crankcase with Pennzoil HM 10w-40 with LC. MPG is 32-36. Yes, MPG is the same or HIGHER. I'm in disbelief myself as my driving style nor gas type has changed as I used the same station and grade for this test. Shell 87 with FP. I was hoping M1 SM 5w-20 would hit near the coveted 40MPG mark. I'm still amazed that a thicker non-PAO gives good MPG as the lighter weights do. Comments, thoughts?