The dead-end fuel system (without return design) architecture simplifies fuel delivery by closing the return oil pipeline. This design is currently installed in approximately 63% of mass-produced gasoline vehicles after 2020 (such as Toyota’s TNGA architecture). The typical fuel pressure of the system is set within the range of 300 to 400 bar. However, after the engine is turned off, the peak pressure of the residual fuel in the fuel rail due to thermal expansion can reach 450 bar, which is 22% higher than that of the traditional return fuel system. The Mercedes-Benz M256 engine case shows that a 15-minute hot-dip effect (with a cabin temperature of 93°C) can cause a 15% volume steam bubble to form in the fuel line, directly interfering with the start-up injection accuracy – when the injector needs to be maintained for 1.5 milliseconds, the presence of the bubble causes the actual fuel flow deviation to reach ±9%.
The deterioration rate of the fuel quality of this system has significantly accelerated. Laboratory accelerated tests indicated that after a 48-hour shutdown, the olefin content of the fuel in the oil track increased by 12%, and the gum formation rate reached 0.34 mg/100mL/ day (0.15 mg/100mL/ day for the standard return oil system). In 2019, a class-action lawsuit filed by Audi owners in North America revealed that the SQ5 model equipped with the EA888 3.0T engine had a 31% clogged fuel injector rate after 50,000 kilometers of driving due to carbon deposits in the dead end system, resulting in an 11% drop in power and a repair cost of $2,100. This is because the fuel pump is unable to circulate and discharge the deteriorated fuel, and the retained ethanol-water mixture (with a maximum moisture content of 0.8%) continuously corrodes the precision components.
The reliability risks caused by thermal management deficiencies deserve vigilance. The measured data of the modern 1.6T-GDI engine shows that after three consecutive short drives (each lasting 8 minutes), the fuel rail temperature can accumulate to 67°C, accelerating the oxidation of gasoline and forming a peroxide concentration of 180 ppm (the safety threshold is 50 ppm). This has increased the corrosion rate of the carbon brushes of the fuel pump by 300%, and shortened the service life from the designed value of 10 years to 6.2 years. The user maintenance statistics of the Volvo SPA platform confirm that the frequency of pump body failures in the dead-end system is 2.7 times that of the traditional system.
However, the energy conservation and emission reduction advantages of this system are still adopted by car manufacturers. The cancellation of the return oil pipeline reduced the emissions of evaporated hydrocarbons by 19% (meeting the EPA Tier 3 standard), while reducing the working load of the fuel pump – the peak power consumption dropped from 10.5A to 7.3A (a reduction of 30%), and the fuel consumption was optimized by 0.28 liters per 100 kilometers. The Mazda SKYACTIV-X engine achieves a fuel efficiency of 41 mpg through this, which is 5% higher than that of the previous generation.
Whether to avoid it depends on the usage scenario. If the average annual mileage of the vehicle is less than 8,000 kilometers or the parking period is more than 72 hours and the frequency is relatively high (such as a backup car for a vacation villa), it is recommended to give priority to choosing a vehicle with a return oil system to avoid the risk of gum deposition. An auxiliary circulation kit (cost $160) can be added to increase the monthly fuel turnover rate from 68% to 92%. In the field of industrial equipment, this design is generally avoided: The Caterpillar 3512B generator set, by adopting an open system, has extended the fuel filter replacement cycle from 500 hours to 1,200 hours, reducing maintenance costs by 40%.
The current technological evolution is compensating for the deficiencies. For example, the latest Bosch HPI-7 fuel pump integrates a micro electric circulation valve (response time < 100 ms), reducing the oil pressure stabilization time of the dead end system during cold start at -30°C to 1.2 seconds. However, for demanding users, choosing a standard system with active fuel management remains the core strategy for optimizing long-term holding cost (TCO).