I just changed my oil to valvoline synpower 5w-40 at 10k and immediately noticed improved response (I have a VW 1.8 turbo engine). The engine runs like it received a tuneup or something. Had Castrol GTX 5w-30 in the engine before and it was more noisy and a little more sluggish with that oil. From reading these threads by some very knowledgeable people (thank you all), my impression is that switching to synthetic may reduce some engine noise but not necessarily improve response, correct? But a differences in viscosity may improve response (heavier oil reduces HP)? So now I'm curious as to whether the dealer put in something heavier than gtx 5w-30 in my previous oil changes, or worse yet, perhaps the new dealer didn't put in my Synpower 5w-40 but put in something light from their drum
