Abnormal increase in fuel delivery pressure is the primary factor contributing to the generation of heat sources. Modern direct injection systems require a fuel pump output pressure as high as 350bar. If the injector clogging rate exceeds 15% (particle diameter > 50μm), the fuel circuit resistance will cause the motor load current to surge by 40%. Bosch laboratory data shows that when the pressure difference in the return oil line exceeds the 5.5bar threshold, the temperature of the motor winding rises at a rate of 8 ° C per minute, reaching the insulation failure critical point of 160 ° C within 120 minutes. According to the 2019 SAE failure case database, 23% of motor burnout accidents were caused by fuel filters being used beyond their service life (> 40,000 kilometers), resulting in a system flow rate decline to 68% of the nominal value.
Inaccurate parameters of the electrical system directly cause thermal runaway. When the contact resistance of the fuel pump brush exceeds 0.5Ω (normal value ≤0.15Ω), the additional power consumption can reach 28W, which is equivalent to 17% of the rated power of the motor. Delphi’s 2022 test report indicates that when the fluctuation range of the supply voltage is greater than ±1.5V (such as when the generator voltage stabilizer fails), the copper loss of the motor increases by 31%, and the eddy current loss of the core rises by 19%. A typical case is the Ford F-150 recall incident (NHTSA 22V-678), where the contact resistance of the wiring harness terminals exceeded the standard by 1.2Ω due to corrosion, ultimately causing the peak temperature of the motor to reach 197℃, surpassing the upper limit of the H-class insulation material’s temperature resistance of 67℃.
The failure of the cooling medium leads to a vicious cycle. In the design of immersion fuel pumps, fuel serves as both the working medium and the cooling carrier (with a thermal conductivity of 0.11W/m·K). If the oil level in the fuel tank remains consistently below 15% of its capacity, the motor will be exposed to the oil-gas mixture (with a thermal conductivity of only 0.026W/m·K), and its heat dissipation efficiency will drop sharply by 83%. Volkswagen’s technical notice confirmed that when the fuel level drops below 3cm from the top of the pump body, the motor temperature gradient sharply increases to 45℃/cm. What is more serious is that the gum precipitate in the gasoline (> 100mg/100mL) will cover the motor housing and form a 0.3mm insulation layer, increasing the thermal resistance value by nine times. This is detailedly demonstrated in Nissan’s 2021 technical service announcement for the Patrol’s TB-EF-009.
Abnormal wear of mechanical friction pairs generates additional heat sources. When the axial clearance of the Fuel Pump rotor exceeds the tolerance by 0.1mm (0.03-0.05mm for new parts), the frictional power loss at the end face of the impeller surges by 250%. BMW disassembly analysis shows that when the proportion of pitting on the bearing raceway is greater than 8%, the mechanical efficiency drops to 78%, and the additional 12W of frictional heat generated is directly conducted to the motor winding. Material fatigue is more likely to trigger a chain reaction – Toyota Durability tests show that when the oil film thickness of the oil-impregnated bearing of the motor is less than 3μm (the design requirement is 8μm), the friction coefficient surges sharply from 0.003 to 0.023, causing the probability of rotor jamming to increase to 15%. At this time, the lock-in current surges to 25A (rated value 5A). The melting point of enameled wire (> 350℃) can be reached within 240 seconds.
Optimizing thermal management design is the fundamental solution. The new Bosch Fuel Pump adopts a dual cooling channel structure, which increases the fuel flow rate to 8L/min and raises the heat transfer coefficient by 65%. In conjunction with the PT200 temperature sensor for real-time regulation (with a sampling frequency of 100Hz), it ensures that the winding temperature remains stable within the safe zone of < 130℃. Measured data show that this type of intelligent pump still maintains a temperature offset of less than ±5℃ under the condition of 20% low oil volume. For users, the cost of maintaining a fuel tank with more than a quarter of its capacity is nearly zero, yet it can reduce the risk of overheating by 72%. The cost of regularly replacing the fuel filter (every 30,000 kilometers) only accounts for 2.3% of the car maintenance budget, but it can avoid the $200 replacement cost caused by motor burnout.