- Hydraulic oil viscosity is incorrect.
- Hydraulic oil level is low.
- The hydraulic oil tank has blockage of suction screens.
- Problems with the hydraulic hoses or hydraulic lines
- The hydraulic oil contains a large amount of air.
- The pump has too much wear.
Note: Ensure that there are no active diagnostic codes for the hydraulic system.
Hydraulic Oil Viscosity Is Incorrect
Make sure that the correct viscosity of oil is in the system. Refer to Operation and Maintenance Manual, "Lubricant Viscosities" for your machine.
The hydraulic oil tank has a sight gauge on the outside of the tank. Check the hydraulic oil level with the machine on level ground and the engine OFF. If oil is NOT seen in the sight glass, the hydraulic oil level is low. Refer to Operation and Maintenance Manual, "Hydraulic System Oil Level - Check" on 953D and 963D machines. Refer to Operation and Maintenance Manual, "Hydrostatic Transmission and Hydraulic System Oil Level - Check" on 973D machines.
Note: Make sure that the strainer is present in the filler tube before adding the recommended hydraulic oil.
If the hydraulic oil level is low, check for oil leakage.
The Hydraulic Oil Tank Has Blockage Of Suction Screens
Inspect the main suction tube for blockages. Inspect the main suction tube for any damage that could restrict the volume of oil that is drawn from the tank. (The suction tube draws oil from the bottom of the tank.) Removing the filler cap and the strainer will allow you to view the inside of the tank. It may be necessary to remove the tank in order to inspect the tank for damage. Refer to Disassembly and Assembly, "Hydraulic Tank - Disassemble" and Disassembly and Assembly, "Hydraulic Tank - Assemble" for your machine.
Problems With The Hydraulic Hoses or Hydraulic Lines
Kinks or restrictions in hydraulic lines or hoses may act like an orifice that creates excessive noise and heat as the high pressure oil is forced through a passage that is smaller than the original opening.
Be sure to check for these conditions on all hydraulic oil hoses, lines, and tubes in the system or the circuit that are in question. Correct any problems that are found. Then retest the hydraulic system for any symptoms.
The Hydraulic Oil Contains A Large Amount Of Air
Ensure that the hydraulic oil is not aerated.
- Check the return lines to the tank for cracks.
- Check all of the fittings and connections for proper torque on the suction side of pumps or on negative pressure side of other motors and other components.
- Check the fluid level sight gauge on the side of the hydraulic oil tank. Check the tank for cracks or leaks. If the hydraulic oil appears cloudy, check the inside of the hydraulic oil tank to ensure that the suction tube and the return oil tube are both in place and that both are submerged in the oil (return oil splashing or spraying back into the tank can aerate oil)
- Examine implement cylinder rod seals for signs of oil leakage or weeping which may allow air to be drawn in when the rod end of the cylinder is below tank/ambient pressure (such as during bucket FLOAT)
- Loosen oil line connections after each hydraulic component (pressure side) and examine the oil for aeration at each inspection point. If the oil appears aerated as the oil seeps out of the loosened connection, that component may be the source of the aeration. The aeration may also be occurring some place between that component and the prior component that showed no signs of aeration
- Examine the suction hose, the main suction manifold, and all suction lines, fittings, and connections from the suction manifold to the steering pump, the fan pump, and the implement pump. Look for indications of oil leakage. If oil leaks from these lines or connections when the machine is shut down, the connections will also draw air into the hydraulic oil system during operation. This condition will cause the pumps to infuse the air and distribute it to the components in that system/circuit and then return the aerated oil back to the tank
- Ensure that the procedure to purge the air from the hydraulic system was completed correctly.
Oil aeration may be caused by a number of factors such as low oil levels in the tank(s), cavitation in pumps or cylinders, worn pump components (shaft seals, port plates, pump housing seals), or leaks in the system on the suction side of pumps. Air in the oil can make the oil more compressible, causing a lag in cylinder movement. Air in the oil can cause erratic operation of hydraulic components.
Examine the hydraulic oil for signs of oil aeration. Aerated oil can appear cloudy if the air is finely diffused in the oil. An oil sample and subsequent oil analysis can determine if the oil is aerated or if the oil is contaminated. If oil aeration is found, the source of the aeration must be located and eliminated.
Repair or replace any suspect components and then retest for the symptom.
Refer to Testing and Adjusting, "Hydraulic Pump - Test and Adjust" for your machine.