Ameer Randolph
There are two types of fuel systems: return fuel systems and returnless fuel systems. In a return system, there are two fuel lines: one that pumps fuel to the engine and another that runs back to the fuel tank to dump excess fuel. In a returnless system, the fuel is pumped back into the tank before reaching the fuel rail. The type of fuel line used depends on the application, with options including metal, rubber, braided, and PTFE-lined fuel lines. Metal fuel lines are generally more durable and compatible with all fuel types, while rubber fuel lines are more flexible and less expensive. Braided fuel lines are flexible and compatible with a wide range of fuels, and PTFE-lined fuel lines are durable, flexible, and resistant to heat and chemical damage.
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What You'll Learn
Return and returnless fuel systems
There are two types of fuel systems: return and returnless. In a return fuel system, fuel is pumped through the pump to the engine, dispensed in the rail, and then there is a line that runs back to the fuel tank to dump the excess fuel back in. The fuel pump is continuously pumping gas through the fuel system at a much higher rate than is actually needed. This keeps the gasoline in the fuel lines cool and flushes out any vapour bubbles that might form. This prevents vapour lock in your fuel system.
Return-style systems require fuel pumps to work all the time, which can shorten the life of the pump. Your plumbing system can also become more complicated as you have to run a separate return line from the regulator to the tank.
In a returnless system, the fuel is pumped back into the tank before the fuel rail. Returnless systems are designed to use the powertrain control module (PCM) to regulate fuel delivery. A fuel pressure sensor mounted to the supply rail of the fuel injectors allows the powertrain control module to monitor the fuel pressure. If the fuel pressure and flow start to decrease as a result of increased engine speed or load, the powertrain control module will compensate by increasing the injector duration and/or operating speed of the fuel pump.
There are two types of returnless systems: mechanical and electrical. Mechanical returnless systems simply relocate the pressure-regulating valve into the fuel tank, directly after the pump. Electrical returnless systems regulate the fuel pump speed in order to control the flow and pressure.
Returnless fuel systems are becoming more common in new vehicles due to tightening federal environmental regulations. They reduce evaporative (EVAP) emissions from the fuel system by keeping the fuel in the tank cooler and minimising evaporation.
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The need for excess fuel
Excess fuel is a result of the fuel pump running at 100% all the time. The pressure regulator determines how much fuel pressure is needed in the line and sends the excess back to the tank. This is done to cool the injectors, the head, the fuel pump, and sometimes the engine computer. The heat is returned through the fuel to the filter and tank, driving out moisture and reducing algae growth. This is especially helpful in cold weather.
In a return fuel system, the excess fuel is pumped through the pump, to the engine, dispensed in the rail, and then there is a line that runs back to the fuel tank to dump the excess fuel back in. This is in contrast to a returnless system, where the fuel is pumped back into the tank before the fuel rail.
The type of fuel line used can also impact the need for excess fuel. Metal fuel lines, for example, are more durable and compatible with all types of fuel, but they are more expensive and less flexible, which can make them harder to install in tight spaces. Rubber fuel lines are more flexible and less expensive, but they are not as durable and may not be compatible with certain fuels or chemicals. Braided fuel lines are flexible, compatible with a wide range of fuels, and have superior connections, but they are prone to leaks if the braid is damaged and may not be suitable for certain chemicals. PTFE-lined fuel lines are very durable, flexible, and resistant to heat and chemical damage, but they are the most expensive option and may not be suitable for certain fuels or solvents.
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Fuel line materials
Fuel lines can be made from a variety of materials, each with its own advantages and disadvantages. The most common materials used for fuel lines are metal, rubber, braided, and PTFE-lined.
Metal fuel lines are typically made from stainless steel, coated steel tube, or aluminum. They are generally more durable than rubber or braided fuel lines as they are resistant to wear and tear and are not prone to cracking or deterioration. Metal fuel lines are compatible with all types of fuel and are generally always a good option. However, they are more expensive, harder to fabricate, and may be difficult to install in tight or hard-to-reach spaces.
Rubber fuel lines are made from rubber or other elastomeric materials. They are generally more flexible than metal or braided fuel lines, making them easier to install. Rubber fuel lines are also typically less expensive than metal or braided lines. However, they are not as durable and can become hard and brittle over time. Additionally, rubber fuel lines may not be compatible with certain fuels or chemicals.
Braided fuel lines are made from a metal or synthetic fiber braid wrapped around a rubber or other elastomeric core. They are more flexible than metal lines and are considered an upgrade as they utilize superior connections. Braided fuel lines are typically compatible with a wide range of fuels but may not be suitable for certain chemicals. They are more expensive than rubber lines but less expensive than metal lines. However, braided fuel lines can be prone to leaks if the braid becomes damaged.
PTFE-lined fuel lines have an inner layer of PTFE (polytetrafluoroethylene), a synthetic fluoropolymer, coated with a layer of braided stainless steel or other metal. They are very durable and resistant to wear, heat, and chemical damage. PTFE-lined fuel lines are also very flexible but may not be as flexible as rubber or braided lines on the outside. They are generally the most expensive option and require special fittings for installation.
Other materials used for fuel lines include nylon tubing, which is a budget-friendly option, and plastic, which is lightweight but melts at lower temperatures and is more difficult to repair. Older vehicles may also have copper fuel pipes, which are easy to fit and repair but are heavy and expensive compared to other options.
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Fuel line durability and flexibility
The durability and flexibility of a fuel line are dependent on the material it is made of. Metal fuel lines are generally more durable than rubber or braided fuel lines, as they are resistant to wear and tear and are not prone to cracking or deterioration. They are also compatible with all types of fuel. However, they are generally more expensive and less flexible, which can make them harder to install in tight or hard-to-reach spaces.
Rubber fuel lines, on the other hand, are more flexible and less expensive, making them a cost-effective solution for replacing fuel lines. They are made from rubber or other elastomeric materials and can be supplied in low pressure (for carburettors) or high pressure (for fuel injection) options. However, they are not as durable as metal lines and can become hard and brittle over time. They may also not be suitable for use with certain fuels or chemicals.
Braided fuel lines are made from a metal or synthetic fibre braid that is wrapped around a rubber or other elastomeric core. They are typically more flexible than metal lines and are compatible with a wide range of fuels. However, they are prone to leaks if the braid becomes damaged, and they may not be suitable for use with certain chemicals.
PTFE-lined fuel lines have an inner layer of PTFE (polytetrafluoroethylene), a synthetic fluoropolymer, which is coated with a layer of braided stainless steel or other metal. They are generally very durable and flexible and are resistant to wear, heat, and chemical damage. They can be used inside and outside the car, as the liner prevents the escape of fuel vapour, eliminating the stale fuel smell inside the car. However, they are typically more expensive than other types of fuel lines.
Plastic fuel lines are lighter than metal tubing, but they melt at lower temperatures and cannot be repaired as easily. They are also not as durable as metal lines and may not be suitable for high-performance applications.
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Fuel line compatibility
Fuel lines are an essential component of any vehicle, delivering fuel from the tank to the engine. They come in a variety of materials, each with its own advantages and disadvantages. The compatibility of a fuel line with a particular fuel or chemical is a crucial consideration when choosing which type to use.
Metal fuel lines, made from materials such as steel or aluminium, are generally compatible with all types of fuel. They are durable, resistant to wear and tear, and not prone to cracking or deterioration. However, they are more expensive and may require proper connections to the fuel tank and engine. Additionally, steel pipes can corrode, leading to fuel leaks.
Rubber fuel lines, on the other hand, are made from rubber or other elastomeric materials. While they are flexible and easy to install in tight spaces, they may not be suitable for all types of fuel and chemicals. Over time, rubber fuel lines can become hard and brittle, and they are less durable than metal lines.
Braided fuel lines, typically made from metal or synthetic fibre wrapped around a core, offer compatibility with a wide range of fuels. They are more flexible than metal lines, but less so than rubber lines, and can be prone to leaks if the braid is damaged. Braided lines are generally considered an upgrade as they flex and utilise superior connections.
PTFE-lined fuel lines have an inner layer of PTFE (polytetrafluoroethylene), a synthetic fluoropolymer, coated with braided metal or other materials. These lines are highly durable, flexible, and resistant to wear, heat, and chemical damage. While they are generally compatible with a wide range of fuels and chemicals, they may not be suitable for certain solvents. PTFE-lined hoses are also effective at preventing the escape of fuel vapour, eliminating stale fuel smells inside the car.
Plastic fuel lines are lightweight and do not perish, but they melt at lower temperatures and are more difficult to repair. Copper fuel lines are easy to fit and repair but are heavy and expensive compared to other options.
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Frequently asked questions
There are two types of fuel systems: return and returnless. In a return system, there is a line that runs back to the fuel tank to dump excess fuel, whereas in a returnless system, the fuel is pumped back into the tank before the fuel rail.
The larger line is the send, and the smaller line is the return.
Fuel lines can be made of materials such as steel, aluminium, rubber, or other elastomeric materials and fibres.
Metal fuel lines are more durable and resistant to wear and tear than rubber or braided fuel lines. They are also compatible with all types of fuel. However, they are generally more expensive and less flexible, which can make them harder to install in tight spaces.
