Like all fuels, Diesel has a natural shelf life. Diesel is considered an organic fuel and like all organics, it decays with age. Diesel can be reliably stored for 12 months at an ambient temperature of 20°C (65°f) and 6 to 12 months at 30°C (86°f).
Emulsified water is absorbed by all types of diesel fuels. This molecular bond can hold with such strength that traditional fuel water separators fail to remove 40% to 100% of emulsified water. Diesel can contain more emulsified water than heavy water that cannot be seen by the human eye. Emulsified water can wear and damage the injection system leading to poor performance or possible engine failure.
Molecules in the fuel lengthen and bond over time creating asphaltenes (diesel sludge). Diesel sludge can clog inline filters and damage critical engine components. As a hygroscopic fuel (one which attracts moisture from the atmosphere) diesel often contains free-standing and emulsified water.