Fuel Lines

Additional Information


The following shop notes describe flexible fuel lines and their installation.‪

Fuel Lines

Flexible fuel lines are used to facilitate connection of lines leading to and from the fuel tank, and to minimize the effects of any vibration in the installation.‪

An 0.080 in. (2.0 mm) restricted orifice is incorporated in the fuel return fitting (upper fitting) at the rear of the cylinder head to maintain fuel pressure in the cylinder head. Do not use restricted fittings anywhere else in the fuel system, and do not substitute a standard fitting for the restricted fitting.‪

The 0.080 in. (2.0 mm) restricted orifice is designed to provide the proper fuel system pressure under all conditions. Do not alter or substitute another size since this may alter engine performance and emissions.‪

When installing fuel lines, it is recommended that connections be tightened only sufficiently to prevent leakage of fuel; thus flared ends of the fuel lines will not become twisted or fractured because of excessive tightening. After all fuel lines are installed, run the engine long enough to determine if all the connections are sufficiently tight. If any leaks occur, tighten the connections only enough to stop the leak. Also check that the fuel filters are tight against the filter adaptors. Do not overtighten filters.‪

High fuel temperatures can cause low power and reduced fuel economy.‪

Detroit Diesel requires that all OEM's follow special fuel line configuration requirements to eliminate high fuel temperature concerns. Some of these configurations are as follows: ‪

  1. A dual draw/dual return style fuel line system should be used with vehicles having dual fuel tank configurations.
  2. When a single tank with a 75 gallon (284 L) or greater capacity is employed, the return and supply line should be at opposite ends of the tank.
  3. When a single tank with less than a 75 gallon (284 L) capacity is used, a fuel cooler is required on the spill side of the fuel system. The fuel cooler should be sized to allow a 40°F (22.2°C) temperature drop under the following conditions with a 1.5 gal/min (5.7 L/min) flow rate:

    Temperature Drop Conditions: ‪

    • 110°F (61°C) Maximum Ambient
    • 180°F (100°C) Fuel Temperature into Cooler

The return fuel line must be connected to the top or face of the fuel tank opposite the pickup line. The fitting should spray the returning fuel along the inside wall of the tank or onto the surface of the fuel to dissipate as much heat as possible. Returning fuel to the bottom of the fuel tank or using a stand pipe is not permitted. ‪

In addition, the fuel return line should be designed to prevent air from bleeding back into the cylinder head fuel passages after the engine is shut down. The possible configurations for this are a looped fuel line or the addition of a fuel check valve (23509140) in the fuel return line. See Figure "Fuel Return Check Valve" .‪

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Figure 1. Fuel Return Check Valve


Specifications can be found in the General Information section at the beginning of the manual. Exceptions are listed below:‪

Exceptions to Standard Fastener Torque Specifications

Exceptions to Standard Fastener Torque Specifications supporting the Series 50 Engine are listed in Table "Exceptions to Standard Fastener Specifications" and also listed in Table "Exceptions to Standard Fastener Torque Specifications" . ‪



Torque, N·m

Torque, lb·ft

Bolt, Injector Clamp‪

M10 x 1.5‪



Table 1. Exceptions to Standard Fastener Specifications



Torque, N ·m

Torque, in. ·lb

Bolt, Turbo Boost Sensor-to-inlet‪

M5 x 0.8‪



Screw, Harness Connector-to-EDU‪




Screw, Harness Connector-to-ECM‪




Screw, Injector Wire Connector‪

M3 x 0.5‪

M3 x 0.5‪


Table 2. Exceptions to Standard Fastener Torque Specifications

Series 50 Service Manual - 6SE50
Generated on 10-13-2008

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