Ok, little update on this one. I spoke to the owner tonight and he's started noticing some gains. He usually sticks £10 a day in his car to get to work, the same journey each day. He said as the week went on he noticed his fuel gauge was reading more and more each day, until he got to friday(today) and didnt need to fill up. From the data id call that a 20% increase, and over the course of a year he's going to be saving around £500 just on his trips to work.