There is a critical risk of material performance degradation in reusing old sealing rings. After five years of contact with alcohol-containing fuel, the volume expansion rate of fluororubber (FKM) seals exceeded 18% (new part standard ≤5%), and the Shore hardness decreased from 75±5 to 58±7 (a decrease of 23%). General Motors’ laboratory thermal aging tests show that when the sealing ring has been in service for 7 years, its permanent compression deformation rate exceeds 65% (the industry’s allowable upper limit is 45%), resulting in a 42% decline in resilience. At this point, if it is forcibly used on the installation surface of the new Fuel Pump, the sealing contact pressure drops from the standard 2.5MPa to 0.8MPa, and the fuel permeability increases to 0.8mL/min (the new sealing ring is only 0.05mL/min), far exceeding the upper limit of 0.1mL/min permitted by the SAE J30 environmental protection regulation.
Microscale deformation directly triggers the leakage path. The nylon-coated sealing ring undergoes axial warping of 0.15-0.3mm under the effect of thermal cycling. When installed on the flange of a new pump, the fit gap can reach 80μm. Detection using a helium mass spectrometer confirmed that such gaps caused an average annual fuel vapor leakage of 17 liters (equivalent to a loss of 22 US dollars in fuel costs), and volatile hydrocarbon emissions exceeded the standard by six times. The 2021 Ford EcoBoost engine recall was clearly attributed to this: reused old sealing rings formed a 0.02mm gap in high-temperature environments, causing the fuel tank pressure to drop from +5kPa to -12kPa, which led to a 90% increase in the trigger rate of the EVAP system fault code P0456.
Material compatibility is more prominent in the new fuel environment. The swelling effect of the current E25 ethanol gasoline on nitrile rubber (NBR) is three times that of ordinary gasoline. Experimental data shows that the volume expansion rate after soaking for 500 hours is as high as 25% (the standard requirement is ≤15%). The actual measurement report of Honda R&D pointed out that before 2010, after the NBR sealing ring of the model came into contact with E15 Fuel, the inner diameter shrinkage rate exceeded 0.4mm (original size Ø62mm±0.2). When installing the new Fuel Pump, an additional 50% indentation force was required, resulting in a 75% increase in the probability of microcracks in the stress concentration area of the sealing groove. This type of crack expands at a rate of 0.05mm per hour under the working condition of 90℃ and develops into a leakage channel within three months.
The decline of sealing performance is positively correlated with safety risks. The high-temperature pressure cycling test (alternating from -30 kpa to +35kPa) confirmed that the compression allowance of the old sealing ring decreased from the initial 1.2mm to 0.3mm after 20,000 cycles. When a vehicle undergoes a side collision (impact acceleration > 15G), the probability of sealing failure of the old sealing ring reaches 32% (for new parts < 1%), and the peak leakage rate is 120mL/s. Statistics from the National Highway Traffic Safety Administration (NHTSA) of the United States indicate that 38% of post-collision fire accidents between 2015 and 2020 were directly related to the failure of fuel system seals.
Cost-benefit analysis supports the replacement strategy. The unit price of new fluororubber seals is only 8 to 12 (accounting for 12,160 of the replacement cost of the oil pump assembly (which requires re-empting the oil tank and replacing parts). The average annual fuel leakage loss is 35%. The repair cost for the damaged EVAP system is 300 yuan. German TUV certification data shows that the use of new sealing rings has extended the service life of the oil pump assembly by 28% and reduced the five-year comprehensive holding cost by 63%. The environmental protection compliance dimension shows more advantages – the new seal controls the evaporative emissions within 20mg per test cycle (the old part reached 180mg), fully meeting the limit requirements of the EU Euro 6d emission standard.