I have a 2006 taurus se with a vulcan which I bought in March of this year. Well I recently just change the O&F in it. Before this the odometer or rather the milage log would read 18-19 avg. MPG. But now it reads 20+ I am running Pennzoil hi milage 5W20 in it, what the prev owner used is unknown by me. Do anyone have any insight into how accurate these MPG calculaters are or how they function?