I just bought a Ford Explorer from a co-worker, it's a 1997 w/4.0 SOHC and 70K in really good condition. It's been well taken care and fed Mobil 1 5w-30 since 5K, changed every 5K like clockwork. I'd really like to keep using Mobil 1 but due to my current stock pile (must be a sickness...but who can pass up a good sale on oil?) of Pennzoil and Chevron I'm going back to dino. Question is with this SOHC engine which weight would be better for a daily driver. I put on 40 miles a day, 30 of which is freeway. Stay with 5w-30 or go to 10w-30 or doesn't it really matter? I believe whatever I use 4K OCI is about right for dino. any thoughts?