Caution: Diesel fuel containing water is still flammable. You could be burned. If you ever try to drain water from the fuel, keep sparks, flames, and smoking materials away from the mixture.

Notice: If there is water in the diesel fuel and the weather is warm or humid, fungus and bacteria can grow in the fuel. They can damage the fuel system. A diesel fuel biocide can be used to sterilize the fuel system. However, the fuel system may still need to be cleaned. Your dealer/retailer can advise you of the appropriate solution.

Sometimes, water can be pumped into the fuel tank along with the diesel fuel. This can happen if a service station does not regularly inspect and clean its fuel tanks, or if it gets contaminated fuel from its suppliers.

If this happens, the water-in-fuel light, if equipped, will come on in the instrument panel. If it does, the water must be drained. Your dealer/retailer can show you how to do this.

If the light comes on, use this chart to determine what action to take.

Notice: Driving when this warning indicator is on, can damage the fuel injection system and the engine. If the indicator comes on right after a refuel, it means water was pumped into the fuel tank. Turn off the engine immediately. Then, have the water drained at once.

To drain water, do the following:

1. Stop and park the vehicle in a safe place. Turn off the engine and apply the parking brake.
2. Remove the fuel cap.
3. Place a fuel-resistant container under the fuel filter. The filter drain valve is located on the bottom of the fuel filter.

If the vehicle has the 6.6L engine, the fuel filter is located in the engine compartment on the driver side of the vehicle. If the vehicle has either the 7.2L or 7.8L engine, the fuel filters are located in the engine compartment on the driver side of the vehicle, and on the driver side frame rail in front of the fuel tank.




4. Open the drain valve by turning two to three turns. When fuel empties from the valve, all the water has been drained. Close the valve hand-tight.
5. Remove the fuel-resistant container and properly dispose of the contaminated fuel. To find out how to properly dispose of contaminated diesel fuel, see Engine Oil .
6. Install the fuel cap.
7. Start the engine and let it run for a few minutes. If the engine stalls, the fuel system may need to be primed. While draining the water from the fuel filter, air may enter the fuel system. If air has entered the fuel system, the fuel system will need to be primed.

If the water-in-fuel light comes on again after driving a short distance or the engine runs rough or stalls, a large amount of water has probably been pumped into the fuel tank. The fuel tank should be purged.

If the vehicle has a Caterpillar® diesel engine, see the Caterpillar® Diesel Engine Operation and Maintenance Manual provided with the vehicle.

If the vehicle has a DURAMAX® diesel engine, in order for the fuel system to work properly, the fuel lines must be full of fuel and contain no air. If air gets into the fuel lines, it will be necessary to prime the fuel lines to eliminate air before operating the vehicle.

Air can get into the fuel lines if any of the following happen:

If one or more of the above occurred, it is very likely that air has entered the fuel system and the fuel system needs to be primed before operating the vehicle.

Air in the fuel lines will not harm the engine or the vehicle. However, the engine may not be able to start until the fuel system is primed and the air is removed.

Priming the 6.6L Duramax® Diesel Engine

If the vehicle is equipped with the 6.6L Duramax® diesel engine, it has a priming pump which is part of the engine mounted fuel filter. The vent valve and the fuel filter primer pump are located on top of the fuel filter housing. The priming pump is hand operated and is designed to bring fuel to the engine to eliminate any air in the fuel lines.

To prime the 6.6L Duramax® diesel engine, do the following:

1. Make sure there is fuel in the tank.
2. Make sure the fuel filter had been installed and properly tightened.
3. Make sure the fuel lines are properly connected and the fuel filter is cool enough to touch.
4. Remove any dirt from the fuel filter head and vent valve by wiping with a cloth.



5. Open the fuel filter vent valve by turning the screw counterclockwise several full turns.



6. Repeatedly push down on the fuel filter primer pump with the palm of your hand. Let the pump return upward between pushes.
7. Operate the priming pump until a small amount of fuel seeps from the vent valve. When fuel is seen, the filter is full of fuel and the system should be primed.
8. Close the vent valve.
9. Clean any fuel that accumulated on the fuel filter.
10. Start the engine and let it idle for a few minutes.
11. Check the filter for leaks.

Priming the 7.8L Duramax® Diesel Engine

If the vehicle is equipped with the 7.8L Duramax® diesel engine, use the following procedure to prime the engine:

1. Make sure there is fuel in the fuel tank.
2. Make sure the specified fuel filter is properly installed.
3. Make sure the fuel lines are securely connected.
4. Make sure the fuel filter is cool to the touch.
5. Use a clean cloth to remove dirt and oil from the fuel filter head and breather valve.
6. Use the palm of your hand to repeatedly press and release the plunger at the top of the fuel filter priming pump. Continue until the plunger resistance becomes firm. This may take from 20 to 100 times, depending upon fuel tank location.
7. Turn the fuel filter breather valve screw counterclockwise several turns to open the breather valve.
8. Use the palm of your hand to repeatedly press and release the plunger at the top of the fuel filter priming pump until fuel begins to seep from the breather valve.
9. Tighten the fuel filter breather screw to the specified torque, 4.9 N·m (43 lbs. in.).
10. Use the palm of your hand to press and release the plunger at the top of the fuel filter priming pump about 20 more times. This sends fuel to the engine.
11. Use a clean cloth to remove any fuel from the fuel filter and surrounding area.
12. Start the engine and allow it to idle for a few minutes.
13. Check the fuel filter for leakage.