Hi Adrian, I had my car terracleaned a year ago, and it made a great difference, both performance and in MPG. The mechanic also advised that I should use premium grade fuel, which I do. The best mpg I have had was a 90 mile trip to Sheffield on the A38 and M1 mostly at 50mph due to roadworks on which I got 53 mpg, and the round trip was 45 mpg without mush speed restriction. Regards, Peter.