Although diesel fuel and water do not readily mix, fuel does tend to entrap moisture from the air each time it is moved from one container to another. Eventually every diesel fuel system collects enough water to become a potential hazard. Fortunately, when it's allowed to settle out, the water will always drop to the bottom of the tank or filter housing. Some diesel fuel filters are equipped with a water drain; a bolt or petcock at the bottom of the housing.
Most 1990-92 diesel engine-equipped vehicles are equipped with a water separator, located in front of the fuel tank under the right side of the vehicle. The water seperator's purpose is to allow water to settle from the fuel right at the tank and to alert the driver when draining is required. When the water level in the separator reaches a certain point, a sensor turns on the glow plug indicator light on the dashboard, causing it to blink continuously. With the introduction of the A3 platform, the water separator was eliminated, and removing water from the fuel system is accomplished with a drain screw on the bottom of the fuel filter.At The Water Separator
- Raise and safely support the vehicle. Remove the fuel filler cap.
- At the separator, connect a hose from the separator drain to a catch pan.
- Open the drain valve (3 turns) and drain the separator until a steady stream of fuel flows from the separator, then close the valve. Don't forget to install the filler cap.
- If the filter is equipped with a water drain at the bottom, place a suitable filter under the filter to catch the water and fuel.
- Remove the retaining clip that secures the control valve (located on top of the filter), then remove the valve, leaving the two lines connected.
- Loosen the drain screw, and allow any accumulated water to flow from the filter. When clear diesel fuel flows from the screw, tighten the screw securely.
- Using a new O-ring, install the control valve, and secure the retaining clip.
- Start the engine and accelerate a few times to clear any air in the system. Check for bubbles, which indicate an air leak in the system.