I have owned this XFE since new delivering its consistent 40-50 mpg up through 110000 miles. At first I would change around 50% oil life with synthetic and the oil looked brand new but then I had to have a timing chain replaced just out of warranty 50/50 deal with Chevy After that it started destroying oil, depending on the oil it gets noisy (metallic timing chain noise) at about 1500 miles and the stuff is black and spent by 3000 sludging my oil filter. (Doesn't seem to matter synthetic or Dino tried a few 40 wt oils but they don't seem to extend the fill just make the car sound better initially) I do find adding a small amount of heavier synthetic 40wt amsoil mid OCI quiets it down a while. I have just been changing the oil a lot to address. I got in on a lot of cheap AAP jugs of assorted pp 10w30 and 5w20 & 5w30 Mobil AP As a result I had leftovers since my decent cars use odd amounts of oil and decided since it's winter and the car does a lot of 5 mile winter trips now that I would just dump the leftovers in a 50/50 mix of Mobil ap 20/30 weights since its likely I have to change sooner than ap is rated for anyway. Car sounds normal and runs normal on this brew. I am curious though will I get better life with ap in the sump? (Never used AP or PP in this car) I would love to extend the fill but more or less have to change oil once it gets noisy and sludgy. Also Could I run PP 10w30 synthetic down to the -25F temps we usually experience or am I correct in keeping lighter oil in the winter? My hope would be 10w30 wouldn't crud up as quickly. The manual lists 10w30 as an acceptable substitute but lists no temperature range. I also have rotella t6 5w40 that I was going to run but I want to clear out the 2 leftover jugs of ap. (Less clutter) before I test it. Any ideas?