We get 3 vehicles serviced at a local mom and pop Shell service station because my dad has known the mechanic there for 20 years. I do change the oil for them once in a while but I generally only do my car and my sister's...for some reason they feel that the inconvenience me when I do oil changes for them and they say, "I'll just take it in to have it done." I've always thought they used Formula shell motor oil there since they put a shell sticker in the window and they're a shell station. However, my dad just dropped our 2003 Chevy Trailblazer 4x4 there for an oil change, and various other maintenance work. When I went to go pick him up I saw a case of oil sitting in the garage through the doors....I had to look closely to see what it said....apparently they use cases of Wolf's Head 5w30 there for oil changes. I was kinda shocked and I've rarely heard of this oil....they probably use it since it's cheap. My dad got his 1997 Chevy S10 2.2L serviced there and the engine ran fine for 150,000 miles before it got totaled, so it can't be THAT bad. Our Chevy Trailblazer has over 40,000 miles on it and the engine is spotless looking through the oil filler and it's only been brought to this place. Anyway, I'm assuming Wolf's Head is an SM approved oil, but does anybody have any opinions about it? Thanks.