Synthetic is great oil...problem is you don't really need oil to be that good, in fact, with 3K - 4K oil changes you would never see a difference as your dino oil won't breakdown in that short a period under normal to heavy wear. Don't believe the marketing hype...too many people get 300K - 400K runnng on dino (it's much better these days too). And if synth really improved your mileage, all the OEM's would long ago have been using/recommending it for the sake of the EPA.