Sylvie Willis
The Vanagon fuel tank is a complex system that has undergone several design changes over the years. The tank's breathing mechanism is influenced by various factors, including its shape, the presence or absence of a pre-filter, and the functionality of the venting hoses and valves. The tank's breathing is also closely tied to the vehicle's fuel pump, with factors such as fuel delivery systems, fuel pressure regulators, and fuel injectors playing a role in ensuring the tank breathes effectively. Understanding the intricacies of the Vanagon fuel tank's breathing mechanism is essential for optimal performance and requires a deep dive into the vehicle's technical specifications.
| Characteristics | Values |
|---|---|
| Fuel tank design | Some Vanagon fuel tanks are flat with a saddle down the middle, while others have an expansion/vapour separator tank above the main tank. |
| Fuel capacity | 2WD models can hold up to 13.5 gallons, while Syncro (4WD) models can hold up to 16 gallons, with the gauge reading above full. |
| Fuel gauge accuracy | The gauges are “indication only” and may not be accurate. The "half tank" reading, for example, may not represent half of the remaining fuel. |
| Fuel pump | The electric fuel pump is controlled by the fuel injection system's electronic control unit (ECU). It moves about 10 times more fuel than the engine uses on average. |
| Fuel filter | Vanagons from 1980 to 1984 had a small square pre-filter with a 7mm inlet and a 12mm outlet. In 1985, VW eliminated the pre-filter and introduced a larger post-filter, which lasts at least 30,000 miles. |
| Venting system | The 2WD Vanagon venting system differs from most cars due to the flat shape of the fuel tank. Venting hoses should be intact and well-sealed to prevent fuel leaks during expansion. |
| Evap canister | A potential issue is a clogged filter, which can cause a pressure difference and a loud clunking noise when the van comes to a stop. |
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What You'll Learn
The 2WD Vanagon's venting system
The 2WD Vanagon tank venting system differs from most cars due to the unusual shape of the fuel tank, which is flat with an inverted saddle shape in the middle. The venting system is critical because liquid gasoline expands a lot when warmed, and there must be room for it to expand without leaking out of the system. The 2WD Vanagon has expansion/vapour separator tanks above the main tank. The venting hoses should be intact and well-sealed, or the expanded fuel will find leaks that are now below the liquid level. The venting lines to the canister are fitted to gravity valves in the top of the expansion tanks. The gravity valves are normally open to breathe freely both ways, but if the vehicle is overturned, they contain a ball that will fall and block the outlet to prevent fuel from running out.
The ventilation system in Vanagons has always been somewhat confusing. Fresh ambient air ventilation is controlled by the four slide levers and rotary fan knob on the dashboard, right next to the radio. These levers have nothing to do with air conditioning if your Vanagon is so equipped. A/C will be addressed later in this article. Fresh ambient air enters the vehicle through the front radiator grille between the headlights. Behind the radiator grill is a smaller grill (about 2" x 24") for fresh air intake, attached to a duct welded to the body. Fresh air flows through this duct to an air distribution box, which is about 1' x 1' x 2' in size, and is buried in the dashboard, dead center about a foot below the windshield. This air distribution box has several cable-controlled flaps on it, and it houses an electric "squirrel cage" fan which is controlled by the rotary fan knob to the right of the slide levers.
Factory-installed air conditioning in Vanagons is a completely separate system from the fresh air system. All air-conditioned air is recirculated air. That is, all the air that is cooled is air that is scooped up from inside the vehicle, cooled, and recirculated back inside the vehicle. It does not work like most other vehicles where one can choose OUTSIDE or INSIDE air to be cooled. There were two different factory-installed AC systems for non-pop-top Vanagons, and two for pop-tops. Vanagon non-pop-top factory A/C: 1980-1984: On early non-pop-top Vanagons up to about 1984, the air conditioning ducting was a plastic monstrosity that came up the driver’s side of the vehicle just behind the driver’s front door, and up over to the passenger side.
There was another A/C system available for the Vanagon that was installed at the dealer. This was an in-dash system. This system placed the evaporator in the dashboard behind the glove box. The outer dashboard vents, instead of being plumbed to the fresh air distribution box, were plumbed to the A/C evaporator. In addition to these vents, two more vents were added either where the radio usually goes, or right next to the radio. If the radio hole was used, the radio was relocated in a plastic enclosure down on the floor in front of the gearshift lever face-up. This system had an overall lower output, but the cold air it did produce was pumped straight at you, so it actually cooled your hot body instantly, as opposed to having to wait for the rear-only A/C to cool the entire interior. These systems are very rare.
A potential problem with the Vanagon evap canister is a clogged filter. The 1989 and later vans have the “clean” side of the can hooked up to a short piece of hose that is shoved into a grommet in the frame. Since this is in the right rear wheel area, there will be dust getting in there. Eventually, the filter inside the can will clog up. Then the top of the fuel tank can be pulled down by the pressure difference when the engine is running and the throttle is above idle. When the van comes to a stop, the vacuum from the engine is shut off and the top of the tank pops back to its normal shape with a loud CLUNK. The cure is to replace the canister and run a hose into the engine compartment (cleaner air) and attach a small filter to the end of the hose. If you are handy, you can add a fitting or piece of metal tube to the air filter box, just like the earlier Vanagons.
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The charcoal canister
The Vanagon's tank venting system is slightly different from most cars due to the unusual shape of the fuel tank, which is flat with a saddle down the middle. The liquid gasoline expands a lot when warmed, so there must be room for it to expand without leaking out of the system. The 2WD Vanagon has an expansion/vapour separator tank above the main tank, which allows for fuel expansion due to temperature changes. The venting hoses should be intact and well-sealed to prevent leaks.
A potential problem with the Vanagon's evap canister is a clogged filter. The cure is to replace the canister and run a hose into the engine compartment, attaching a small filter to the end.
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Fuel tank expansion
Cavitation occurs when the fuel pump is starved for fuel, creating a buzzing noise and negatively impacting the pump's cooling and lubrication. To mitigate this, VW eliminated the pre-filter and increased the size of the hose and nipple between the tank and the pump, ensuring an ample fuel supply. However, the flat tank design still poses challenges when it comes to fuel expansion.
Liquid gasoline expands significantly with temperature changes, and without adequate expansion space, this expansion can lead to leaks. The 2WD Vanagon addresses this with expansion/vapor separator tanks above the main tank. These tanks provide the necessary expansion room, preventing fuel from escaping through leaks.
The venting hoses and valves play a crucial role in the expansion process. They must be intact and well-sealed to allow the expanding fuel to vent properly. The venting lines are connected to gravity valves in the expansion tanks, which open in both directions under normal conditions. However, in the event of a vehicle rollover, these valves contain a ball that will block the outlet, preventing fuel from running out.
Maintaining the venting system is essential to ensure proper fuel tank expansion. Simple tests, such as pulling a vacuum on the vent line and opening the fuel filler cap, can verify the integrity of the venting network. Additionally, visual inspections may reveal the need to replace or freshen up hoses and grommets.
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Fuel gauge calibration
To calibrate a fuel gauge, it is necessary to perform at least 20 dosed fuel fillings, as specified in the fuel gauge passport. This involves filling the tank with a specific amount of fuel, waiting for the fuel to settle and the foam to disappear, and then recording the fuel level in the tank. For example, for a 600-liter tank, one dosed fill would be 30 liters, so the tank would need to be filled 20 times with 30 liters each time. This process helps to create a calibration table that correlates the level of fuel in the tank with its volume.
After calibration, it is important to perform a control drain or refueling to verify the correctness of the data. This step can take anywhere from 20 to 50 minutes. It is worth noting that some companies may charge a fee for fuel tank calibration but may not actually perform the necessary steps, instead only installing an ROV and setting the MIN/MAX values. To ensure proper calibration, request a tare table from your service provider. A properly calibrated fuel gauge will have a calibration table with more than 2 values.
Additionally, it is important to adhere to the regulations and recommendations of fuel level sensor manufacturers during the calibration process. Using certified measuring tanks and high-precision calibration stations can help ensure the reliability of the data.
For specific vehicle models, such as the Mk4 complete kit, the calibration process may involve plugging a button into the back of the fuel gauge and programming empty and full levels accordingly. Other models, such as the Ford E7ZZ-9275-A sending unit for 1987-1993 5.0 Mustang, may require calibrating to a specific ohm range. It is always best to refer to the specific instructions for your vehicle's make and model.
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Fuel pump issues
One of the main issues with the fuel pump in Vanagons is cavitation, which occurs when the pump does not receive enough fuel at the inlet side due to obstructions or a clogged filter. This can cause the fuel pump to make a buzzing noise and lead to lubrication and cooling issues, as the fuel flowing through the pump is also responsible for keeping it cool and lubricated. In some cases, the pre-filter, small tubing size, and flat design of the 2WD Vanagon fuel tank contributed to cavitation. VW eventually eliminated the small pre-filter and increased the size of the hose and nipple between the tank and the pump to ensure an ample fuel supply.
Another common reason for fuel pump failure is a dirty fuel supply or debris in the pump, which can cause clogging and damage to the pump. It is important to ensure that the fuel tank and all associated seals and breather lines are clean and free of rust, dirt, or other contaminants. If the fuel tank is not properly maintained, it can lead to repeated pump failures.
Additionally, the layout of the fuel tank and pump can impact their performance. In 2WD Vanagons, the relatively flat fuel tank is not much higher than the fuel pump, which can affect the fuel supply to the pump. In contrast, Syncro (4WD) Vanagons have the fuel tank directly above the fuel pump, which works more efficiently.
To troubleshoot fuel pump issues, it is recommended to check for any buzzing noises, indicating cavitation. If cavitation is occurring, replacing or cleaning the filter, or both, may be necessary. It is also important to inspect the fuel tank and associated components for any signs of dirt or debris and to ensure that the venting network is airtight and clear.
If the fuel pump fails completely, it will need to be replaced. The process for replacing the fuel pump in a Vanagon involves disconnecting the battery, clamping shut the hose from the fuel tank, and removing the old pump by detaching the nut for the bracket, electrical connections, and fuel hose connections. It is important to have a backup fuel pump or a new fuel pump readily available to avoid being stranded in case of pump failure.
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Frequently asked questions
To test that the vent line is clear, pull vacuum on the vent line, and then open the fuel filler cap, which should release the vacuum.
The venting network allows for fuel expansion due to temperature changes. Liquid gasoline expands a lot when warmed, so there must be room for it to expand without leaking out of the system.
The fuel gauge in a Vanagon is meant to indicate how close the vehicle is to being empty. However, it is important to note that the gauges are not always accurate, and the “half tank” reading may not actually be half of the remaining fuel.
The cure is to replace the canister and run a hose into the engine compartment, attach a small filter to the end of the hose, or add a fitting or piece of metal tube to the air filter box.
