Gasoline that has been stored for a long time (usually more than 3 to 6 months) will undergo significant chemical deterioration, forming highly viscous deposits that directly threaten the core components of the oil circuit system. The peroxide concentration generated by the fuel oxidation reaction can increase by 50% after 60 days of storage. When the content of the formed viscous gel exceeds 5mg/100ml, it reaches a high-risk level. Laboratory tests of the American Automobile Association (AAA) show that in ordinary E10 ethanol gasoline stored for 12 months, the number of insoluble colloidal particles increases by more than 300%, and the peak particle size is concentrated in the range of 2-5 microns. When these particles accumulate on the surface of the Fuel Pump motor commutator to a thickness of more than 0.1mm, It will cause the contact resistance of the carbon brush to increase by 40%, resulting in a fluctuation range of ±15% in the armature working current, significantly shortening the service life of the electric pump. Statistics show that oil pump failures caused by old gasoline gum account for approximately 22% of all fuel system failures, with an average repair cost ranging from 400 to 800 US dollars.
The phase separation problem of ethanol gasoline aggravates the risk of system corrosion. After being stored in a high-humidity environment for 60 days, E10 gasoline (containing 10% ethanol) can absorb more than 0.5%vol in moisture. The ethanol-water stratification process increases the ethanol concentration in the aqueous phase to 70-85%. The pH value of this mixture drops to the range of 4.8-5.5, and the corrosion rate can reach three times that of ordinary gasoline. Chrysler’s technical notice states that the phase-separated liquid will cause pitting pits with a diameter of 20-50μm on the surface of key components of the plunger pump (such as the stainless steel plunger) within 7 days, resulting in the fit clearance of the plunger pair expanding from the design value of 3-5μm to 8-12μm, and reducing the volumetric efficiency by more than 15%. Maintenance data in the North American region shows that ethanol gasoline leads to a fuel pump assembly replacement rate that is approximately 18% higher than in other regions.
Microbial contamination forms biofilms in old fuel oil, blocking the oil passage. When the density of the fungal/bacterial community breeding in the fuel reaches 10³ CFU/ml, a biofilm can be formed within 72 hours. The report of the American Society for Testing and Materials (ASTM) shows that such biofilms can reduce the effective pore size of the filter screen by more than 60%, forcing the working pressure of the oil pump to increase from the standard 3.5 bar to 4.8 bar, and the temperature of the motor winding rises by 20-30°C accordingly. Volkswagen confirmed in its large-scale recall in North America in 2021 that fuel contaminated by microorganisms covered 90% of the oil pump filter screen, causing a 45% reduction in fuel flow and subsequently leading to poor acceleration faults in approximately 175,000 vehicles.
Wear particles accelerate the mechanical wear of precision components. When the hardness of abrasive impurities (including silicoaluminates and rust particles) in old fuel reaches 6-7 on the Mohs scale and the concentration of particles with a particle size distribution within the range of 5-15μm exceeds 50ppm, it is equivalent to containing 3,000-5,000 hard particles per milliliter of fuel. Bench tests of Bosch high-pressure pumps have shown that such contamination can lead to an 8-fold increase in the wear rate of the plunger pair. After 10,000 kilometers of operation, the critical mating surface will develop scratch grooves with a depth of 3-7μm, causing the standard deviation of pressure fluctuations in the high-pressure system to increase from ±2 bar to ±8 bar. Internal statistics from Ford Motor Company indicate that for vehicles that have been using inferior fuel for a long time, the average lifespan of their high-pressure fuel pumps has shrunk from the designed value of 150,000 kilometers to less than 80,000 kilometers, and the probability of premature failure has increased by 65%.
Systematic oil product management is needed to prevent damage from aging gasoline. The U.S. Department of Energy suggests that the storage period of gasoline be controlled within 90 days and that stabilizers containing polyetheramine (PEA) components be added, which can reduce the rate of gum formation by up to 80%. Regularly carrying out cleaning and maintenance of the fuel system, cleaning the fuel tank and fuel lines every 24,000 kilometers, can reduce the risk of fuel pump blockage failure by 70%. Although choosing fully synthetic engine oil that meets the API SP standard cannot directly protect the oil pump, it can indirectly extend the service life of the fuel system by approximately 20% by optimizing the overall lubrication environment. When a vehicle is parked for a long time, keeping the fuel tank more than 95% full can effectively reduce the oxygen concentration in the tank space by 40% and delay the oxidation process of the fuel.