On equipment, hydraulic fluids are used for
hydraulic systems that steer, lift, push, close, and so
forth. Hydraulic fluids that are currently in use include
mineral oil, vegetable oil, water, phosphate ester,
ethylene glycol compounds, and oil in water. The three
most common types of hydraulic fluids are water base,
petroleum base, and synthetic base.
NOTE: Before adding hydraulic fluid in a piece of
equipment, consult the operators manual for the type of
hydraulic fluid required. Using the incorrect type can
contaminate the hydraulic system which requires that
the system be drained, flushed, and refilled with the
NOTE: Before adding gear oil, consult the
operators manual for the type of oil required for the
specific type of equipment. Mixing different types of
gear oil may cause the oil to break down and not have
the quality required to protect the gears.
Figure 1-42.-Filter system configurations.
Gear oils are used in both manual transmissions and
differentials. Gear oils reduce friction and do not break
down or foam at high temperatures.
Two filter system configurations are in use today:
the full-flow system and the bypass system.
FULL-FLOW SYSTEM. All the oil in the full-
flow system (fig. 1-42, view A) is circulated through the
filter before it reaches the engine. When this system is
used, it is necessary to incorporate a bypass valve in the
oil filter. This valve allows the oil to circulate through
the system without passing through the element in the
event that it becomes clogged. This factor prevents the
oil supply from being cut off from the engine.
BYPASS SYSTEM. The bypass system (fig. 1-42,
view B) diverts only a small quantity of the oil each time
it is circulated and returns it directly to the oil pan after
it is filtered. This type of system does not filter the oil
before it is sent to the engine.
Grease is used to lubricate bearings, bushings, and
pivot points. For inaccessible bearings, grease is applied
under pressure by the use of a grease gun (fig. 1-43).
Figure 1-43.-Hand-operated grease gun.