953D, 963D and 973D Track-Type Loaders Hydraulic System Oil Temperature Is High Caterpillar


Hydraulic System Oil Temperature Is High
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1.1. Probable Causes
2.1. Recommended Actions
3.2. Oil Cooler Core is Plugged or Air Flow Over The Core is Low
4.2. Thermal Bypass Valve Is Stuck And/Or The Cooler Is Inefficient
5.2. Viscosity Of The Oil Is Wrong
6.2. The Hydraulic Oil Contains A Large Amount Of Air
7.2. System Pressure Is Low
8.2. Hydraulic Oil Level is Low
9.2. The Fan Pump Has Too Much Wear
10.2. The Demand Fan Is Not Operating Properly
11.2. Problems With The Hydraulic Hoses and Hydraulic Lines
12.2. The Outside Temperature Is Too Hot
13.2. Temperature Sensor Is Not Operating Properly

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

Personal injury or death can result from escaping fluid under pressure.

Escaping fluid under pressure, even a very small pin-hole size leak, can penetrate body tissue and cause serious injury and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury.

Always use a board or cardboard when checking for a leak.


Use this procedure in order to troubleshoot high hydraulic oil temperature or use this procedure if one of the following event codes is active.

Table 1
Event Codes  
Code and Description  Conditions which Generate this Code  System Response 
E878 High Hydraulic Oil Temperature  System temperature exceeds 80° C (176° F) The code is logged. 

Probable Causes

  • Oil cooler core is plugged or air flow over the core is low

  • Thermal bypass valve is stuck and/or the cooler is inefficient

  • Viscosity of the oil is wrong

  • The hydraulic oil contains a large amount of air

  • System pressure is low

  • Hydraulic oil level is low

  • The fan pump has too much wear

  • The demand fan is not operating properly.

  • Problems with the hydraulic hoses and hydraulic lines

  • The outside temperature is too hot

  • Temperature sensor is not operating properly.

Recommended Actions

Note: Care must be taken in order to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the machine. You must be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component that contains fluid. Dispose of all fluids according to local regulations.

Oil Cooler Core is Plugged or Air Flow Over The Core is Low

Check for restrictions in the core of the oil cooler. Air flow that is generated from the fan travels through the cooler fins in order to carry the heat away from the oil. High temperature can be caused by blockage of the fins of the cooler core. Ensure that the fins of the cooler core are clean. Ensure that the fins of the cooler core are not restricted. Check and clean any buildup of debris from the exterior of the cooler core, the fan, and/or the fan shroud. Clean the oil cooler core or repair the oil cooler core.

Periodically clean the cooling fins of the hydraulic oil cooler core. Clean the cooling fins of the hydraulic oil cooler core more frequently if the operating environment contains contamination and debris (wood chips, debris from landfills, coal dust, etc) that can easily clog the fins.

Use a bent copper tube that is approximately 1/4 to 3/8 inch diameter as an extension to the air nozzle. This will facilitate cleaning of the middle spaces. Blow out the core with compressed air. Move the air nozzle in a systematic pattern so that the air flow covers the whole core that includes areas in the corner. Clean the middle space between the hydraulic oil cooler and the radiator cores.

Do not use steam or high pressure water for frequent cleaning . If steam or high pressure water is required in order to dislodge any debris that is held deep in the cores, ensure that the cleaning is thorough. This may require partial removal or total removal of the hydraulic oil cooler for better access.

Incomplete cleaning with water may cause remaining debris to harden in place. Use lights and wire probes in order to ensure that the cleaning is thorough and complete.

If the debris has hardened in the center of the cores, these cores may need to be removed for cleaning. If you use a degreaser and steam for removal of oil and grease, wash the core with detergent and hot water. Thoroughly rinse the core with clean water. Dry the cores completely before operating the machine in the work mode.

Thermal Bypass Valve Is Stuck And/Or The Cooler Is Inefficient

Check the thermal bypass valve and/or cooler efficiency. If the thermal bypass valve of the hydraulic oil cooler is stuck in the OPEN position, the oil is not being directed through the cooling tubes. This prevents the hydraulic oil cooler from sufficiently cooling the oil. If the fins on the hydraulic oil cooler are clogged with debris, the hydraulic oil cooler may not be operating in an efficient manner in order to cool the oil.

With an infrared thermometer, test the temperature of the cooler inlet and the cooler outlet. A temperature differential of at least ten degrees should be observed, once the hydraulic oil is warmed to approximately 63° C (145° F). Closing temperature for the thermal bypass valve is 62° C (143° F) to 65° C (149° F). Opening pressure for the bypass valve is 620 kPa (90 psi) at 71° C (159° F). Replace the bypass valve if the temperature difference between the inlet of the bypass valve and the outlet of the bypass valve is not great enough.

Note: If replacing the bypass valve does not correct the problem, the cooler core may be clogged with contaminants. This condition may be present after a catastrophic failure of a hydraulic pump, motor or other hydraulic component that would release particles and contaminants into the system. The cooler core must be cleaned or the cooler core must be replaced.

Viscosity Of The Oil Is Wrong

Ensure that oil is the correct viscosity for the operating conditions. In order to determine the correct oil viscosity, refer to the Operation and Maintenance Manual, "Lubricant Viscosities and Refill Capacities" for your machine.

The Hydraulic Oil Contains A Large Amount Of Air

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. 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 seeping 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.

System Pressure Is Low

Check the system pressure. Refer to Testing and Adjusting, "Hydraulic Pump - Test and Adjust" for your machine.

Hydraulic Oil Level is Low

Check the oil level. Add oil, if necessary. Refer to Operation and Maintenance Manual, "Hydraulic System Oil Level - Check" for the 953D and 963D machines. Refer to Operation and Maintenance Manual, "Hydrostatic Transmission and Hydraulic System Oil Level - Check" for the 973D machines.

The Fan Pump Has Too Much Wear

Refer to Testing and Adjusting, "Hydraulic Pump - Test and Adjust" for your machine.

The Demand Fan Is Not Operating Properly

Check the demand to make sure its not operating properly. Check all the fan components that your machine is equipped with. Components that your machine may be equipped with include the clutch, motor, manifold and solenoid. Be sure to check the solenoid current in ET. Repair or replace any components, if necessary. Refer to Systems Operation, "General Information (On Demand Fan)" for your machine for more information.

Problems With The Hydraulic Hoses and 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 Outside Temperature Is Too Hot

  • If the machine is equipped with a demand fan, check the demand fan to make sure it is operating properly. Recalibrate the demand fan if necessary.

  • On the 973D machine only, inspect the belt condition. If the belt shows any wear or damage then replace the belt.

  • If the machine is being operated in extreme temperature conditions then change the current operation of the machine.

Temperature Sensor Is Not Operating Properly

Check the air inlet, hydraulic oil and coolant temperature sensors in ET to make sure the sensors are operating properly.

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