SPECIFICATIONS

Vehicle Systems Testing And Adjusting
Hydraulic Oil Temperature
(Too Hot)
When the temperature of the hydraulic oil gets over
98.8C (210d), polyurethane seals in the system
start to fail. High oil temperature causes seal failure
to become more rapid. There are many reasons why
the temperature of the oil will get this hot.
1. Hydraulic pump is badly worn.
2. Heavy hydraulic loads that cause the relief valve
to open.
3. The setting on the relief valve is too low.
4. Too many restrictions in the system.
5. Hydraulic oil level in the tank is too low.
6. High Pressure oil leak in one or more circuits.
7. Very dirty oil.
8. Air in the hydraulic oil.
NOTE: If the problem is because of air in the oil, it
must be corrected before the system will operate at
normal temperatures. There are two things that
cause air in the oil (aeration). These are:
a. Return oil to the tank goes in above the level of
the oil in the tank.
b. Air leaks in the oil suction line between the pump
and the tank.
Mast and Carriage
Problem: The hydraulic system will not lift the
load.
Probable Hydraulic Cause:
1. There is an air leak, which lets air into the
hydraulic system on the inlet side of the hydraulic
pump.
2. The relief valve opens at low oil pressure.
3. The hydraulic pump has too much wear.
4. The load is not correct (too heavy).
Probable Mechanical Cause:
1. The mast is not in alignment with the other lifting
components and does not move freely.
2. Not enough lubricant on the parts of the mast that
move.
3. The carriage or mast rollers (bearings) are worn
and do not move (seized).
Problem: Lift cylinder extends too slowly.
Probable Hydraulic Cause:
1. Not enough oil supply to lift cylinder.
2. Defective lift cylinder seals.
Probable Mechanical Cause:
1. The mast is not in alignment with the other lifting
components and does not move freely.
2. Not enough lubricant on the parts of the mast that
move.
3. The carriage or mast rollers (bearings) are worn
and do not move (seized).
Problem: Mast does not move smoothly.
Probable Hydraulic Cause:
1. Air in the hydraulic system.
2. Relief valve sticks or defective.
Probable Mechanical Cause:
1. Not enough lubricant on the parts of the mast that
move.
2. Load rollers (bearings) defective or not adjusted
correctly.
Problem: Mast will not lower completely or will
not lower at all.
Probable Mechanical Cause:
1. Lift cylinder damaged or bent.
2. Load rollers (bearings) defective or not adjusted
correctly.
3. Not enough lubricant on the parts of the mast that
move.
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