There are a number of companies that sell “Cetane Boosters” - additives that are poured into the tank of a diesel powered vehicle and which supposedly not only improve the MPG and power, but also clean and lubricate the injectors, remove water from the tank, make the exhaust sweet smelling, make your teeth whiter and your hemorrhoids shrink. Okay – I made up the last three, but you get the point. So, are these really worthwhile or just snake oil?