Wow, thanks for the replies guys!
The 2007 Prius calls for a 5,000 mile OCI. 2010+ Prius changed to 10,000 miles (different engine). Of course, the 5,000 OCI for my 2007 Prius was based on conventional oil. I change my oil at 7,500 miles and have had used oil analysis done on it. Of course, as you'd imagine, its in cherry condition with almost no wear metals and lots of TBN. When the oil gets changed at 7500 miles it is almost as clean as it went in - the car seems to be very easy on oil, and I havent had any problems with fuel dilution.
The engine runs probably 85% of the time. It does shut off at red lights and once you start moving it usually restarts. The RPM's are generally low, I am a lead foot so I do hammer it a few times a week to pass a slow-poke or merge onto the highway. But generally cruising at 45mph, the engine might be turning 1,000 rpms. So I can see that being a factor.
Some owners of the Prius have used synthetic all of the cars life and still get oil burning/coke up rings.
Ive been using M1 products with the Prius, but have no loyalty - I will use whatever synthetic is available at Wal-mart or I can buy Amsoil as a local dealer lives nearby. What I dont want to do, is use M1 with high VI and even though the used oil analysis turn out nice, the ring lands are gumming up over time vs. using PU or Amsoil signature that wouldnt do the same.
And to the person who said 1/4 qt per 3000 miles isnt anything to worry about, I agree. Its miniscule considering the Prius only takes 3.5 quarts in the sump. I dont want it to evolve from 1/4qt per 3,000 miles to 1qt every 1,000 miles like some Prius owners though.
I guess the new question is, knowing that M1 has viscosity improvers and those can increase gum/carbon on the rings, which oil has the least VI and has the most potential to keep the rings and lands the cleanest?
