Most all new cars recommend energy conserving oil as stated in the api donut on oil bottles. I recently switched from GC to synpower 5w30 because of mpg issues. Immediately i noticed the motor was smoother and seemed to rev faster and MPG shot up. I did a little snooping and noticed that 40*/100* celcius visc. were not all that different between the two oils. Obviously the GC was developed for european specs. I did notice that Gc does not have the energy conserving verbage in the API donut on the bottle. What are the characteristics of this oil that make it so. Gc in fact to me seems almost like an early to mid 30 weight oil not the almost 4 weight everyone portrays it to be.