TM 5-3895-359-14&P
INSTRUMENTS AND TACHOMETER DRIVE
The instruments generally required in the operation of a
Oil pressure gages have male threads and require
diesel engine consist of an oil pressure gage, water
female fittings.
temperature gage, an ammeter and a mechanical
Water Temperature Gage
tachometer. Also, closely related and installed in the
general vicinity of these instruments are controls
The engine coolant temperature is registered on the
consisting of an engine starting switch, an engine stop
water temperature gage.
knob and an emergency stop knob (Fig. 1).
Incorrect coolant temperature readings will be registered
Anti-Vibration Instrument Mountings
if the gage assembly is incorrectly installed or the
capillary tube is damaged.
Anti-vibration mountings are used in many places to
absorb engine vibration in the mounting of instruments,
To prevent damage to the gage assembly from
drop relays, tachometers, etc. When it may become
vibration, the capillary tube must be securely fastened to
necessary to service a part secured by rubber mounts,
the engine the full length with suitable clips at intervals
care should be exercised, during removal and
of ten inches or less. Sharp bends in the tube must be
installation of the part, so twist is not imposed into the
avoided, particularly at the gage or bulb connection
rubber diaphragm. At the time the part is removed from
areas. Where the tube must be bent around any object,
the engine for service, the mounts should be inspected
the bend must not be less than one inch radius.
for damage and replaced, if necessary.
Any extra length can be taken up by coiling, the
The attaching screw, through the center of the mount,
diameter of which should not be less than two inches. e
must be held from turning during final tightening of the
coils must be located so that they may be securely
nut. Support the screw and tighten the nut only. If this
fastened to prevent vibration.
screw turns, it will pre-load the rubber diaphragm in
torsion and considerably shorten the life of the mount.
The ammeter is wired into the electrical circuit to show
Oil Pressure Gage
the current flow to and from the battery. After starting
The oil pressure gage registers the pressure of the
the engine, the ammeter should register a high charge
lubricating oil in the engine. As soon as the engine is
rate at rated engine speed. This is the rate of charge
started, the oil pressure gage should start to register. If
received by the battery to replenish the current used to
the oil pressure gage does not register at least the
start the engine. As the engine continues to operate,
minimum pressure listed in the Operating Conditions on
the ammeter should show a decline in the charge rate to
the battery. The ammeter will not show zero charge rate
cause of the low oil pressure determined and corrected
since the regulator voltage is set higher than the battery
before the engine is started again.
voltage. When lights or other electrical equipment are
connected into the circuit, then the ammeter will show
discharge when these items are operating and the
engine speed is reduced.
Tachometer
The tachometer, driven by the engine, registers the
speed of the engine in revolutions per minute (rpm).
Fig. 2 - Typical Engine Starting Motor Switch.
Fig. 1 - Typical Instrument Panel.
10-8-18
