Well, it's coming about time to change my oil in my old Corvette. When I noticed the price of M1 SS went down from $4.78 to $3.78 per qt, I decided that was what I was going to run. But I'm having second thoughts. My engine was rebuilt about 12k mi ago (since Nov) and I did not ask or get the clearances, but I believe it to be a bit loose. With the current 10w40 oil, I see 20psi hot idle (800 RPM) oil pressure. I do not want to chance it with a xw30 oil in this engine, but I don't really want to run the 15w50 M1 either (and am too cheap to pay $5 for the 0w40 M1). I have an 8 qt (with filter) oil capacity. I was thinking of running the Pennzoil 15w40. The car does not have cats. It's on the high side of the 40 weight which is good, but with the colder weather coming up, I looked down the aisle and saw an 8 pack of regular Pennzoil for $9.44 ($1.18 per qt!). Now, I'm thinking of running regular Pennzoil 10w40 during the winter (vis 118/12.5 @40C/100C) and 15w40 (vis 88/13.5 @ 40C/100C) during the summer months. I may also consider using a little AutoRx in each change to keep things clean. What do you think? I've been a syn user for too many years now to cross back, but I think the SL dino oil may just be a better bang for the buck.