The Stratus has had SM/GF-4 Castrol GTX for the past few thousand miles. Overall, it's a good oil, I'm sure, but I was more impressed with the SM/GF-4 MaxLife and the SL/GF-3 Mobil-1 RedLine combo (3.5:1). All were 5W-30. The GTX had the most clicking noises at startup, which are not noticable with MaxLife, and only slightly with the M1+RL combo. The engine felt like it didn't rev up as quickly with the GTX. Also, the extreme cold starting was much better with MaxLife and the best with the M1+RL. For the current prices I see for regular GTX ($1.92), it should be a good oil, but I spent $.20 more per quart for MaxLife this time. For $1.92, I will be looking for other oils. Although at $1.12, the SM/GF-4 Trop Artic is very appealing! And when the SM/GF-4 Mobil-1 arrives, granted it is a new formulation, that will again be the choice pick.