Ammeter
An ammeter measures current flowing to and from
the battery. When the batteries are charging, the
meter needle moves to the plus side of the gauge;
when the batteries are being discharged, the needle
moves to the minus side. A consistent negative read-
ing when the engine is running indicates a possible
problem with the charging system.
Application Air Pressure Gauge
An application air pressure gauge registers the air
pressure being used to apply the brakes, and should
be used for reference only. The gauge will not regis-
ter air pressure until the foot brake pedal is de-
pressed or the trailer hand brake is applied.
Coolant Temperature Gauge
NOTICE
A sudden increase in coolant temperature may
indicate engine or cooling system failure. Bring
the vehicle to a safe stop and investigate the
cause to prevent further damage. Do not operate
the engine until the cause has been determined
and corrected.
During normal engine operation, the coolant tem-
perature gauge should read between 175 and 195°F
(79 and 91°C). If the temperature remains below
160°F (71°C), inspect the cooling system to deter-
mine the cause.
If the temperature exceeds the maximum tempera-
ture shown in
Table 2.3
, inspect the cooling system
to determine the cause. See the
Century Class
Trucks Workshop Manual
for troubleshooting and
repair procedures.
Maximum Coolant Temperature
Engine Make
Temperature: °F (°C)
Caterpillar
215 (101)
Cummins
225 (107)
Detroit
215 (101)
Mercedes-Benz
221 (105)
Table 2.3, Maximum Coolant Temperature
If coolant temperature rises above the maximum
temperature listed in
Table 2.3
on EPA07 engines,
the CHECK engine lamp will illuminate. If the condi-
tion does not improve, the STOP engine lamp will
also illuminate and an audible warning will sound.
The engine will then derate or shut down, depending
on the type of engine protection system installed.
Drive Axle Oil Temperature Gauges
NOTICE
A sudden increase in oil temperature that is not
caused by a load increase may indicate mechani-
cal failure. Bring the vehicle to a safe stop and
investigate the cause to prevent further damage.
Do not operate the vehicle until the cause has
been determined and corrected.
During normal operation, forward-rear and rear-rear
axle oil temperature gauges should read between:
•
160 to 220°F (71 to 104°C) for Meritor
™
drive
axles;
•
180 to 200°F (82 to 93°C) for Dana Spicer
®
drive axles.
Under heavy loads, such as when climbing steep
grades, temperatures that exceed the normal oil tem-
perature range for a short period are not unusual. If
the temperature returns to normal when the load de-
creases, there is no problem.
Engine Oil Pressure Gauge
NOTICE
A sudden decrease or absence of oil pressure
may indicate mechanical failure. Bring the vehicle
to a safe stop and investigate the cause to pre-
vent further damage. Do not operate the engine
until the cause has been determined and cor-
rected.
The engine oil pressure gauge displays the current
engine oil pressure. If engine oil pressure falls below
the minimum levels shown in
Table 2.4
, the CHECK
engine lamp will illuminate. If the condition does not
improve, the STOP engine lamp will also illuminate
and an audible warning will sound. The engine will
then derate or shut down, depending on the type of
engine protection system installed.
Instruments and Controls Identification
2.16
