How to Purge Air From a Fuel Filter on a Diesel

Written by grace mclain
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How to Purge Air From a Fuel Filter on a Diesel
(Comstock/Comstock/Getty Images)

The fuel filter on a diesel engine cannot contain any air or it can cause vapour lock. Vapour lock can cause the engine not to crank at all. The diesel fuel system is designed to keep air out of the fuel system by keeping the entire system full of diesel at all times. Air can get into the fuel system after a fuel filter change or if the vehicle runs out of diesel. If there is air in the fuel system, do not continue to crank the engine until the system is full of diesel again.

Skill level:

Things you need

  • 1/2-inch drive ratchet
  • Metric socket set
  • Clean rags
  • Fresh diesel

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  1. 1

    Park the vehicle in a safe and well-ventilated work area. Engage the parking brake and turn the engine off.

  2. 2

    Open the bonnet and locate the diesel fuel filter canister. Most diesel engines have the fuel filter canister mounted to the rear driver-side of the engine.

  3. 3

    Unscrew the cap from the fuel filter canister with the ratchet and a socket. Then, pull the cap off with the fuel filter attached to the bottom of the cap. Place the cap on a clean rag.

  4. 4

    Pour the fresh diesel into the fuel filter canister until the canister is completely full of diesel. Then, slide the cap with the fuel filter back into the canister. Screw the cap on tight. Then, tighten down the cap with the ratchet and socket.

  5. 5

    Turn the ignition key to the accessory position for 30 seconds. Then, turn the key off again. Turn the key to the accessory position again for 30 seconds. This process will finish priming the fuel filter and the fuel lines with diesel and remove any air from the fuel system. Crank the engine and let it run for about one minute to completely cycle the diesel throughout the engine.

  6. 6

    Turn the engine off and try cranking the engine again. Make sure to turn the key to the accessory position for at least 15 seconds before each crank. Then, turn the engine off and close the bonnet.

Tips and warnings

  • When the key is in the accessory position for 30 seconds, the diesel is pumped out of the fuel tank and into the fuel filter canister. The diesel then fills the canister up as well as the fuel lines. This process removes the air from the fuel system by replacing the air with diesel.
  • Keep all open flames away from diesel.
  • Wear safety glasses when replacing the fuel filter.

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