Join Date: Jan 2005
Location: Las Vegas, Nevada, USA
Here is what I found out.
Yes, Gasoline does have an expiration date. When gasoline is stored, gums will form, the result of copper-catalyzed reactions of the unsaturated HCs. Antioxidants and metal deactivators are added to slow this down, but after six months the fuel has degraded enough to be no longer good for use. Another problem with gasoline aging is many of the performance and octane additives such as aromatic hydrocarbons evaporate and leave a fuel that delivers less performance than fresh fuel.
Why are there seasonal changes in Gasoline?
Only gaseous hydrocarbons burn, consequently if the air is cold, then the fuel has to be very volatile. But when summer comes, a volatile fuel can boil and cause vapor lock, as well as producing high levels of evaporative emissions. The solution was to adjust the volatility of the fuel according to altitude and ambient temperature. The oil companies without informing the public of the changes have automatically performed this volatility change for decades. It is one reason why storage of gasoline through seasons is not a good idea. Gasoline volatility is being reduced as modern engines, with their fuel injection and management systems, can automatically compensate for some of the changes in ambient conditions - such as altitude and air temperature, resulting in acceptable driveability using less volatile fuel.