Hey guys I know you get asked the same questions over and over again but I thought I would see what your opinions were. I have a 1996 Ford F-150 4x4 5 speed with the 300 efi straight six in it. The truck has 101,000 miles on it. I just recently bought the truck and I have no idea whats been ran through it. So I thought I might experiment with something new. I have always ran Castral GTX, mainly just because thats what my dad always ran and he would have killed us if we ran anything different he always talks about when he was a mechanic how he ran other oils mainly Pennziol when he would have to pull heads they would be nasty and he experimented by not cleaning anything and running Castral for a few oil changes and took the head back off and it was really clean. So ever since he has been a die hard Castral fan. But that was years ago and times have changed so I thought I might try something else. I was wondering what you guys thought the best oil to run in it would be. I have never tried senthetic oil but I have been thinking really hard on it. The 300 will be ran fairly hard and I live in Missouri so we have cold and hot weather. Every brand says there oil is better but I know alot of you guys have put them to the test. My brothers opinion is run full synthectic Super Tech and change it every 3000 miles which would cost close to the same as running any other synthetic oils for 5000 miles. He ran some test on several different oils when he was in Linn State Tech school And believe it or not Supertech came out on top. You always here that walmart spends most of the money on making there oil instead of advertisment and thats why its alot cheaper. But I never could make my self buy it lol.