Ameer Randolph
Saddle fuel tanks are used in cars and boats. They are called 'saddle' fuel tanks because they use two wells, one on either side of a driveshaft or exhaust system, resembling a saddle. This style of tank optimises luggage compartment capacity, fuel volume and crash safety. In cars, the fuel pump picks up fuel from both sides of the tank. In boats, the setup may include a selector valve with the option to have tank 1, tank 2, or both tanks. However, this may result in the motor drawing fuel unevenly from the tanks.
| Characteristics | Values |
|---|---|
| Number of wells | Two |
| Position of wells | One on either side of a driveshaft or exhaust system |
| Optimisation | Luggage compartment capacity, fuel volume and crash safety |
| Appearance | One fuel tank from the top |
| Primary side | Contains the pump that provides pressure to the fuel rail |
| Secondary tank | Contains a transfer or jet pump |
| Fuel system | Returnless, regulating pressure to the fuel rail inside the tank |
| Fuel level senders | Used to determine fuel level in the tanks for distribution, instrument panel readings and EVAP testing |
| Fuel movement | Fuel pump picks up fuel from both sides of the tank |
| Fuel pump replacement | Often unnecessary, as behaviour of fuel wells, pumps and sending units is misdiagnosed |
| Fuel pressure | Excessive voltage drops or inconsistent fuel-level readings may indicate ground connections and wiring harness issues |
| Fuel tank setup | Selector valve allows for drawing fuel from tank 1, tank 2, or both |
| Fuel burn | One tank may feed faster than the other, resulting in an imbalance |
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What You'll Learn
Fuel transfer between the two wells
Saddle fuel tanks, also known as saddle-style tanks, are commonly used in automobiles and boats. They are characterised by their structure, which consists of two wells or tanks positioned on either side of a driveshaft or exhaust system. This design optimises luggage compartment capacity, fuel volume and crash safety in cars.
Now, let's delve into the intricacies of fuel transfer between the two wells of a saddle fuel tank:
Firstly, it's important to understand that the two wells of a saddle fuel tank do not inherently equalise fuel levels. In other words, the fuel does not automatically flow between the two wells to maintain the same level in both. This is a common misconception, and it's important to clarify that fuel transfer between the wells is facilitated by specific mechanisms and systems.
In most modern saddle fuel tank systems, the primary objective is to maintain as much fuel as possible in the primary tank. This serves the purpose of keeping the primary pump submerged in fuel, ensuring it remains cooled. As the engine burns fuel, the system transfers fuel from the secondary tank to the primary tank. This process continues until the secondary tank is empty, at which point the fuel pump module draws fuel solely from the primary tank.
The primary tank typically has a fuel pump module that connects to the vehicle's serial data bus. This primary pump provides pressure to the fuel rail. Usually, the primary tank is filled first when fuelling the vehicle. The secondary tank, on the other hand, houses a transfer pump, also known as a jet pump. This transfer pump plays a crucial role in facilitating fuel movement between the two tanks.
In some vehicles, the system is designed to balance the fuel distribution between the two tanks to optimise weight distribution. This balancing act is achieved through the use of fuel-level sender units present in both the primary and secondary wells. These sender units provide critical information about the fuel levels in the tanks, aiding in fuel distribution, instrument panel readings, and EVAP testing.
It's worth noting that some older saddle fuel tank systems employed a return line mechanism. In this design, a suction jet utilises the venturi effect created by the returning fuel to draw fuel into the primary fuel well. Additionally, certain boats with saddle tanks may have a selector valve that allows the operator to choose between drawing fuel from tank 1, tank 2, or both tanks simultaneously. However, ensuring an even draw from both tanks during operation can be challenging.
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Fuel pump functionality
Saddle-style fuel tanks are used in several car models and optimise luggage compartment capacity, fuel volume, and crash safety. They consist of two wells, one on each side of the driveshaft or exhaust system. From the bottom, you will see two tanks, a primary and a secondary tank. The primary tank usually has a fuel pump module that connects to the vehicle over a serial data bus. This pump provides pressure to the fuel rail and is typically the side that the fuel inlet fills first. The primary pump is kept submerged in fuel to keep it cool.
The secondary tank contains a transfer pump, sometimes called a jet pump. This pump draws fuel from the secondary tank to the primary as the fuel is burned. The secondary pump may also be used to test the functionality of the pump and senders. Modern saddle-style tanks use a returnless fuel system that regulates the pressure to the fuel rail inside the tank. This system uses the extra blowout fuel to power a venturi-type suction that pulls fuel from the passenger side of the tank.
Older systems with a return line may use a suction jet that employs the venturi effect to suck fuel into the primary fuel well. This effect is created by the returning fuel. Both the primary and secondary wells contain fuel-level sender units that determine the fuel level in the tanks. These sender units are critical to the operation of the fuel system and are used for fuel distribution, instrument panel readings, and EVAP testing.
Ground connections and wiring harness issues are common problems for saddle-style tanks. If there are excessive voltage drops or inconsistent fuel-level readings, the connections at the body and chassis grounds should be checked for excessive resistance. The top of the tank may collect road salt and deicing brines that can cause shorts to the ground.
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Fuel tank wiring issues
A saddle fuel tank is a unique design that allows for a more efficient use of space in a vehicle. It consists of two separate tanks connected by a transfer tube, and it sits over the drive shaft like a saddle on a horse, hence the name. The wiring of a saddle fuel tank system is an important aspect that ensures the proper functioning and safety of the fuel system. Here are some key points to consider regarding fuel tank wiring issues:
The wiring harness is a critical component that connects the fuel pump, sending unit, and other sensors in the tank to the vehicle's main electrical system. It supplies power and grounds the components, ensuring they function correctly. A faulty or damaged wiring harness can lead to a host of issues, including fuel gauge inaccuracies, pump malfunctions, and even potential safety hazards. Corrosion or damage to the wiring harness due to fuel exposure is a common issue. The wiring harness is often submerged in fuel, and over time, the fuel can degrade the wiring insulation, leading to short circuits or open circuits. This can cause fuel pump failure, inaccurate fuel level readings, or even fuel leaks, creating a fire hazard.
Ensuring proper grounding is crucial for the fuel tank wiring system. Inadequate grounding can lead to electrical noise, which may affect the performance of the fuel pump and sending unit. It can also result in inaccurate fuel gauge readings and, in some cases, damage to electrical components. When installing or repairing the wiring harness, it is important to use the correct wire gauge and type. Using wires that are not designed for fuel tank environments, such as those that are not fuel-resistant, can lead to safety issues. The wrong wire gauge may also affect the performance of the fuel pump and sending unit due to insufficient power delivery.
Finally, during the installation or replacement of a saddle fuel tank, it is important to ensure that the wiring harness is properly secured and routed. Improper routing can lead to chafing or damage to the wiring, causing short circuits. Additionally, ensuring that the wiring is secured properly prevents unnecessary strain on the connections, which could lead to intermittent or complete loss of function. Regular inspection and maintenance of the wiring harness and connections are crucial to prevent issues. Over time, vibrations and movement of the vehicle can loosen connections or cause wear and tear on the wiring, leading to potential malfunctions or safety hazards.
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Fuel tank design and capacity
Saddle-style fuel tanks have been used in several car models over the past decade. This style of tank uses two wells, one on either side of a driveshaft or exhaust system. From the top, it looks like one fuel tank, but from the bottom, you will see two tanks. The primary side usually has a pump that provides pressure to the fuel rail and is typically the side that the fuel inlet fills first. The secondary tank contains a transfer pump, sometimes called a jet pump.
The capacity of saddle fuel tanks varies depending on the specific application and requirements. For example, in the context of cars, the capacity of each well in a saddle-style tank can range from 40 to 50 gallons, as mentioned in a boat-building discussion. In another instance, a boat captain mentions having eight fuel tanks with a total capacity of 99,000 gallons, with a burn rate of 40 gallons per hour at idle and 180 gallons per hour at 75% power.
In the case of industrial fuel storage, Newberry offers double-wall saddle fuel tanks that meet UL-142 standards for aboveground storage of flammable and combustible liquids. The capacities of these tanks range from 3000 to 20,000 gallons, with the option of even larger sizes.
The design of saddle fuel tanks optimises fuel volume, and in the case of automobiles, it also improves luggage compartment capacity and crash safety. The two-well design allows for more fuel to be stored compared to a single-tank system, and the distribution of the fuel across two wells can also help balance the weight distribution in the vehicle.
Modern saddle-style tanks often employ a returnless fuel system that regulates pressure to the fuel rail inside the tank. This setup helps manage fuel levels and pressure, ensuring efficient fuel distribution and engine performance.
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Fuel tank maintenance
Regularly Inspect and Clean the Tank
Over time, debris, contaminants, and water can accumulate in the saddle fuel tank. This can lead to corrosion, affecting the tank's integrity and performance. Regularly inspecting and cleaning the tank can help prevent such issues. Use a suitable cleaning solution and follow the manufacturer's guidelines for cleaning intervals.
Monitor Fuel Levels and Pressure
Saddle fuel tanks have two wells, and it's important to monitor the fuel level in each well regularly. Inconsistent fuel-level readings may indicate an issue with the fuel senders or wiring harness. Additionally, keep an eye on fuel pressure. Low fuel pressure can be caused by clogged fuel filters, a faulty fuel pump, or leaks in the fuel line.
Test the Fuel Pumps and Senders
The primary and secondary fuel pumps and senders are critical components in a saddle fuel tank system. Test them regularly to ensure they are functioning correctly. Use a fuel caddy to drain the fuel and then pump it into the secondary tank to observe if the fuel is transferred to the primary tank. This test helps determine if the pumps and senders are working properly.
Prevent Salt and Brine Buildup
The top of the saddle fuel tank can collect road salt and de-icing brines, which can cause electrical shorts. Regularly inspect and clean the top of the tank to prevent such buildup, especially after driving in winter conditions where salt and brine are commonly used on roads.
Maintain the Fuel System
The fuel system, including the fuel lines, filters, and injectors, should be maintained per the manufacturer's recommendations. This includes regular cleaning and replacement of filters, as well as checking for leaks and clogs. Maintaining the fuel system ensures optimal fuel flow and engine performance.
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Frequently asked questions
A saddle fuel tank is a tank that uses two wells, one on either side of a driveshaft or exhaust system.
The fuel pump picks up fuel from both sides of the tank.
You can set up a saddle tank by using a selector valve with the option to have tank 1, tank 2, or both tanks.
Ground connections and wiring harness issues are common problems for saddle-style tanks.
