I was reading a post about 10W-30 being a good oil for Texas. Well, how about California? We've got some hot summers here. I also live in the mountains where the winters means snow and ice (below freezing, but not by much). My manual recommends 10W-30. I have 150,000 miles. What should I use? I was thinking about Mobil 1 10W-30. (I am aware of the risk of leaking seals) What do you guys think? Also, is it safe to use oil different from what the manufacturer recommends for the engine?