I bought a 1997 F150 4X4 with the 4.6 Triton and about 130K miles. Well, basically I want to know what is the best oil to run on it, consider these things guys. 1. I have no clue the previous owner used for the first 130K miles. 2. Under the hood it calls for 5W30 3. Summer just started this week here in Oklahoma City, it will probably be 95 - 105 for a long time. 4. When winter comes should I stick with the same kind of oil (5W30)? we go down to single digits at times and I have to start this thing very early in the morning since I go in at 4:30 AM to work. Also, I just put some 5W20 synthetic blend in it (dont ask why, shoulda been 5W30 I know) do I need to change this ASAP? Ive been thinking of shelling out the cash for the $4.99/Quart Mobil 1, I want this engine to last as long as it can. Thanx in advance to all that help.