Second post! Woo-hoo! I WANT to settle on one oil! I am not interested in switching back and forth between viscosities. I currently have 2 Volvos in the stable. My wife's '99 V70 XC and my '05 S80. Both cars have a 2.5T turbo engine. Acceptable viscosities are 5w30, 10w30 and 5w40. Her older car "recommends" 10w30, and mine "recommends" 5w30, both with 7500 OCIs. The weather here in Savannah is moderate, rarely freezing in the winter but the summers can get quite hot. Am I better off using a 10w30 year-round since our winters are fairly mild and the oil will stand up to the winter heat, or can the 5w30 handle the heat of the summer just as well? As far as oils, she is approx. 6000 miles into a 15,000 mile OCI with EP 10w30. Normally I don't let it go that long but I'm curious to do a UOA. After that I'm switching her to Maxlife Synthetic with 7500 OCIs. I realized I enjoy changing oil too much to wait 15,000 miles. I'm running SynPower, but plan on switching to QS HP after that's finished. Or what if I ditch both 30s and go with M1 0w40? I like that it's A3 rated, but will I take a noticeable hit in fuel economy?