I drive a Seat Exeo Diesel and am very impressed by the speed Tec. The engine is quieter and also accelerates better! I had the problem in the winter that my diesel always jerked slightly in lukewarm state, after the addition of Speed Tec that was fixed immediately. In my opinion, the effect lasts so max. 3 tanks of fuel. If you naturally drives the tank is empty it takes away immediately! I am very enthusiastic about the speed Tec!