330D, 336D and 340D Excavators Hydraulic System – Main Hydraulic Pump Air – Purge

When the main pumps have been serviced or the hydraulic oil has been replaced, remove the air from the main pump. Remove the air from the main pump in the following manner:


Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.

Refer to Special Publication, NENG2500, “Caterpillar Dealer Service Tool Catalog” for tools and supplies suitable to collect and contain fluids on Caterpillar products.

Dispose of all fluids according to local regulations and mandates.

------ WARNING! ------

Personal injury can result from hydraulic oil pressure and hot oil.

Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system.

Make sure all of the work tools have been lowered to the ground, and the oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.


    Illustration 1 g01418346

    Pump compartment

    (1) Plug

    (2) Case drain hose

    (3) Pressure tap

  1. While the engine is stopped, remove plug (1) .
  1. Fill the main pumps with oil.
  1. Install plug (1) . Tighten plug (1) securely.


    To avoid system damage, make sure that the hydraulic pump is properly filled with hydraulic oil before start-up.

  1. Start the engine.
  1. Place the engine at low idle position. Raise the boom and hold the boom in this position.
  1. Slowly loosen case drain hose (2) until oil begins to flow around the hose connection.
  1. Tighten case drain hose (2) to the specified torque.
  1. Stop the engine and slowly lower the boom until the work tool is on the ground. This pressurizes the hydraulic tank.
  1. Connect 6V-4143 Quick Connect Coupler and 177-7860 Hose Assembly to pressure tap (3) until oil begins to flow from the open end of the hose.
  1. Remove the quick coupler and hose assembly from pressure tap (3) .