Gasoline Quality & Extended Storage Periods

    Although gasoline does not technically "spoil", its quality does deteriorate when it is stored for extended periods.  Most refiners assume that from  the time gasoline is manufactured until the time it is used in a vehicle will be about 90 days.  Various gasoline characteristics are based on this assumption.  There are basically three areas of concern when gasoline is stored for extended periods,  They are stability volatility, and moisture.

Gasoline Stability

    Gasoline oxidizes while in storage.  When gasoline is stored for extended periods f time, this oxidation results in gasoline that will create gummy deposits in  the fuel induction system.  Severe cases can even result in fuel filter plugging.

    In those instances where gasoline is stored for extended periods, such as private fleet storage, fuel stabilizers should be added.  Fuel stabilizers extend the storage life of gasoline and reduce its tendency to cause induction system deposits. An appropriate additive package should be available from the fuel supplier.

Gasoline Volatility

    Gasoline volatility is adjusted based on the season in which it is to be used.  Fuels for cold weather use are made more volatile to provide good cold start and warm up performance. Summer fuels are made less volatility to minimize hot drivability problems and vapor lock.

    When fuels are stored for long periods of time, they may ultimately be used in a climate other than that for which they were designed.  In these cases vehicle performance can suffer.

    As an example, gasoline purchased in late March would typically be a winter grade gasoline.  If this fuel were still in use months later (July), the fuel would be to volatile for the climate.  The vapor pressure if this fuel could easily be 3.5 to 4.5 psi higher than fuels then available.  This excessive volatility could result in greater incidences of hot start/hot drivability problems.  Conversely summer fuels stored for several months and then used in colder months would provide poor cold start and poor warm up performance.
 

Gasoline Moisture Content

    Many of today's gasolines contain ethanol to improve octane quality or for environmental reasons.  Proper quality control procedures eliminate concerns about ethanol's sensitivity to water.  However when gasoline/ethanol blends are stored for several months, they may encounter excessive moisture due to condensation inside the storage tank or from other sources.  If this moisture level becomes high enough there is the possibility that the ethanol and moisture could "phase separate" and go to the bottom of the tank.  Proper inventory turnover is necessary to ensure that ethanol blends do not pick up excess moisture.

Summary

    As can be seen from the above examples, gasoline inventory should be turned over on a regular basis to minimize a variety of potential problems.  By turning gasoline supply over on a regular basis (once every two months or less) problems relating to stability (gum deposits), volatility, and fuel moisture content can be minimized.