Fuel Return Line: Description and Operation

Nylon Fuel Pipes

Nylon fuel pipes are designed to perform the same job as the steel or rubber fuel pipes they replace. Nylon pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There are two sizes used: 3/8" ID for the fuel feed, and 5/16" ID for the fuel return.

The fuel feed and return pipes are assembled as a harness. Retaining clips hold the pipes together and provide a means for attaching the pipes to the vehicle. Quick-connect type fittings are used at the ends of the fuel feed/return pipes and at the in-line fuel filter. They are described in the next paragraph. Sections of the pipes that are exposed to chafing, high temperature or vibration are protected with heat resistant rubber hose and/or corrugated plastic conduit.

Nylon fuel pipes are somewhat flexible and can be formed around gradual turns under the vehicle. However, if forced into sharp bends, nylon pipes will kink and restrict fuel flow. Also, once exposed to fuel, nylon pipes may become stiffer and are more likely to kink if bent too far. Special care should be taken when working on a vehicle with nylon fuel pipes:

CAUTION: To Reduce the Risk of Fire and Personal Injury:

^ Always cover nylon fuel pipes with a wet towel before using a torch near them. Also, never expose the vehicle to temperatures higher then 115°C (239°F) for more than one hour, or more than 90°C (194°F) for any extended period.
^ Take care not to nick or scratch the nylon fuel pipes. If damaged, they must be replaced.

Quick-Connect Fittings


Quick-connect type fittings provide a simplified means of installing and connecting fuel system components. Depending on the vehicle model, there are two types of quick-connect fittings, each used at different locations in the fuel system. Each type consists of a unique female connector and a compatible male pipe end. 0-rings, located inside the female connector, provide the fuel seal. Integral locking tabs or fingers hold the fittings together.


Engine Fuel Pipe 0-rings


Fuel feed and return pipe connections at the fuel metering system are sealed with replaceable 0-ring seals. These 0-ring seals are made of special material, and should only be serviced with the correct service part.


Vapor Pipes and Hoses


The vapor pipe extends from the fuel sender assembly to the charcoal canister. It is made up of sections of steel pipe and connected to the fuel sender and charcoal canister with fuel resistant rubber hoses.