Originally posted by amartinson
Not trying to be a smarty pants, but if the stuff is being added to the tanker or at the refinery, why do people feel the need to add 8 more oz. at the pump?

Aftermarket Additives It would be convenient for the user if a finished diesel fuel could satisfy all his or her requirements without the use of supplemental additives. Although this is often the case, some users must use additives because the low temperature conditions in their region are more severe than those for which the fuel was designed, or because of other special circumstances. Other users feel that they need a higher quality diesel than regular diesel.

A large number of aftermarket additive products are available to meet these real or perceived needs. Some are aggressively marketed with testimonials and bold performance claims that seem "too good to be true." So, as with any purchase, it is wise to remember the advice, caveat emptor – let the buyer beware.

It may be helpful to regard additives as medicine for fuel. Like medicine, they should be prescribed by an expert who has made an effort to diagnose the problem. And they should be used in accordance with the recommendations of the engine manufacturer and the instructions of the additive supplier. Sometimes indiscriminant use of additives can do more harm than good because of unexpected interactions.