The Function and Common Symptoms of a Faulty Fuel Return Line

The fuel return line is a hose that returns excess fuel from the engine to the fuel tank where a fuel pressure regulator is used.

Fuel injection systems may or may not have return lines. Mechanical diesel fuel systems with an injector pump always have a return line that must never be pinched or clogged. Electronic diesels may or may not have a fuel return system. So what is a fuel return line, anyway?

Fuel injection systems may or may not have return lines. Mechanical diesel fuel systems with an injector pump always have a return line that must never be pinched or clogged.

– Richard McCuistian, ASE Certified Master Automobile Technician

What’s the Function of a Fuel Return Line?

Modern gasoline powered vehicles are equipped with fuel injection, and fuel injection systems may or may not have a return line type fuel system.

Vehicles equipped with return-type fuel systems have a drawback over modern returnless fuel delivery systems. After passing through the engine, the fuel returns to the tank hotter. This can raise the temperature of the fuel in the tank, which can affect the fuel’s combustibility and the vehicle’s overall efficiency.

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: The continual heating and cooling of the fuel on return systems slightly alters the chemical properties of the fuel, so a returnless system is better.

Returnless fuel delivery systems allow fuel to be colder, resulting in better fuel economy and emissions. The heat inside the fuel tank also makes fuel evaporate more, putting more strain on a vehicle’s evaporative emissions (EVAP) control system and potentially creating an emissions problem.

It’s also very common on MPI platforms to have returnless systems with a fuel rail pressure sensor that provides fuel rail pressure feedback input to the PCM. The current feed to the fuel pump will be manipulated to control fuel pressure by a fuel pump control module or the ECM/PCM itself.

GDI systems have a mechanical high pressure fuel pump driven by the camshaft. These high-pressure fuel pumps have an integral solenoid and a fuel rail pressure sensor to fine tune the high fuel rail pressure, but the high pressure pump always receives its fuel from a low pressure pump in the fuel tank.

Faulty Fuel Return Line Symptoms

A faulty fuel return can have major ramifications for your vehicle’s functionality and safety. Make sure to look out for the following signs:

Fuel Leaks

Fuel leaks can occur if the fuel return hose gets punctured or worn out. A leaking gasoline return pipe can cause fuel to accumulate under the car and create a strong fuel smell. Leaking fuel should be taken seriously because a small spark can cause a fire.

Sometimes a kink in the fuel return line can also cause the engine to produce strong fuel odors without necessarily creating a leak.

Vapor Lock

When a faulty fuel return line prevents fuel from returning to the fuel tank, then vapor lock can occur. Vapor lock happens when fuel turns into gas after it heats up due to close exposure to the engine. Vapor lock is typically accompanied by performance problems such as misfires, poor acceleration, and reduced fuel efficiency.

A Note About Carburetor Vehicles and Fuel Return Lines

There are return and returnless fuel systems, but carburetor vehicles don’t have fuel return lines unless the carburetor is fed by an electric fuel pump. The fuel pressure regulator on a carbureted engine has very little effect because the electric pump is fairly weak.

The ones that do will run just fine with the return line disconnected and capped, because the fuel reservoir on a carburetor works like a commode tank, with a float and a needle and seat. Carburetors only receive about 5 psi of fuel pressure for that reason, but no return line is necessary for a carburetor system.

The fuel return line plays an essential role in engine operation and performance. When it breaks, it can become a safety threat. If you suspect a problem with your fuel return line, don’t hesitate to ask a competent mechanic to check your vehicle.

Get the Right Fuel Return Line For Your Vehicle

A bad fuel return line can cause fuel leaks and poor engine performance. You should replace this component immediately to keep your vehicle running smoothly. It’s a good thing CarParts.com allows you to shop for the right fuel return line in just a few clicks.

Here at CarParts.com, you can order a fuel return line for your vehicle with just a few clicks. Simply enter your vehicle’s year, make, and model in our vehicle selector, and we’ll show a list of compatible fuel return lines from the leading aftermarket manufacturers. Our distribution centers are strategically located, so you can expect your new part to arrive in as fast as two business days.

You don’t have to delay your repair because CarParts.com can deliver the part that you need quickly. Check out our selection of fuel return lines and enjoy low prices when you shop now at CarParts.com.