Air intake restriction vacuum is measured in inches
of water (inH
2
O). For vehicles equipped with a
graduated indicator or a restriction gauge on the
dash, check the gauge with the engine off. If the
yellow signal stays locked in the red zone once the
engine is shut down, or is at or above the values
shown in
Table 3.1, the air cleaner element needs to
be replaced.
Air Intake Maximum Restriction Values (inH
2
O)
Engine Make
GHG14, GHG17, and
GHG21 Engines
Cummins 25
Detroit 18
Table 3.1, Air Intake Maximum Restriction Values
NOTE: Rain or snow can wet the filter and
cause a temporary high reading.
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. See
Fig. 3.34. The gauge
will not register air pressure until the foot brake pedal
is depressed 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
temperature gauge should read 175 to 195°F (79 to
91°C). If the temperature remains below 160°F
(71°C), inspect the cooling system to determine the
cause. See
Fig. 3.35.
For Detroit engines, if coolant temperature rises
above the maximum temperature listed in
Table 3.2,
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.
02/12/2015 f090514
Fig. 3.33, Air Intake Restriction Indicator, Graduated
f61138010/31/2016
Fig. 3.34, Application Air Pressure Gauge
f61178008/16/2019
Fig. 3.35, Analog Coolant Temperature Gauge - ICUC
Instruments
3.19
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