NOTE: Rain or snow can wet the filter and
cause a temporary high reading.
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 yel-
low signal stays locked in the red zone once the en-
gine is shut down, or is at or above the values
shown in
Table 4.2, the air cleaner element needs to
be replaced.
Vehicles may be equipped with a go/no-go restriction
indicator without graduations (see
Fig. 4.6) instead of
a graduated indicator.
Air Intake Maximum Restriction Values (inH
2
O)
Engine Make EPA10 Engines GHG14 Engines
Cummins 25 25
Detroit 22 18
Table 4.2, Air Intake Maximum Restriction Values
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, as shown in
Fig. 4.7, should read
175 to 195°F (79 to 91°C). If the temperature re-
mains below 160°F (71°C), inspect the cooling sys-
tem to determine the cause.
If coolant temperature rises above the maximum
temperature listed in
Table 4.3, the CHECK engine
lamp will illuminate. If the condition does not im-
prove, 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 en-
gine protection system installed.
Maximum Coolant Temperature
Engine Make Temperature: °F (°C)
Caterpillar 230 (110)
Cummins 225 (107)
Detroit 215 (101)
Mercedes-Benz 222 (105)
Table 4.3, Maximum Coolant Temperature
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, drive axle oil temperature
gauges (see
Fig. 4.8) should read between 160 and
220°F (71 and 104°C).
04/08/2005 f090431
Fig. 4.6, Manual-Reset Air Restriction Indicator, Go/
No-Go
10/09/2001
f610565
WATER
100
150
200
250
F°
Fig. 4.7, Coolant Temperature Gauge
Instruments
4.9
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