Specifications
Vehicle System Testing & Adjusting 48
Hydraulic Oil Temperature (Too Hot)
When the temperature of the hydraulic oil gets over
98.8°C (210°F), 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.
Hydraulic System and Mast
During a diagnosis of the hydraulic system,
remember that correct oil flow and pressure are
necessary for correct operation. The output of the
pump (oil flow) increases with an increase in motor
speed (rpm) and decreases when motor speed
(rpm) is decreased. Oil pressure is caused by
resistance to the flow of oil.
Visual checks and measurements are the first step
when troubleshooting a possible problem. Then do
the Operation Checks and finally, do instrument
tests with pressure gauges.
Use the Fittings Gauge, a stop watch, a magnet, a
thermometer and a mm (inch) ruler for basic tests to
measure:
1. The pressure of the oil to open the relief valve.
Relief valve pressures that are too low will cause
a decrease in the lift and the tilt characteristics of
the lift truck. Pressures that are too high will
cause a decrease in the life of hoses and
components.
2. Drift rates in the cylinders. Cylinder drift is
caused by a leakage past cylinder pistons, O-ring
seals in the control valve, check valves that do
not seat correctly or poor adjustment or fit in the
control valve spools.
3. Cycle times in the lift and tilt circuits: Cycle times
that are too long are the result of leakage, pump
wear and/or pump speed (rpm).