TRUCK SERVICE MANUAL
when engine is new to serve as a guide for indication of
Instrument and Control Group 15
progressive engine condition. Instruments and gauges
show at all times how to get the most satisfactory service
from an engine. Safety controls are used on Cummins
Rated engine speed is the rpm attained at full load.
Engines to shut down the engine because of high coolant
Governed engine speed is the highest rpm a properly
temperature, low or loss of lubricating oil pressure and
adjusted governor will allow the engine to turn, no load.
engine speeds above rated rpm.
Governed engine speed must never be exceeded on
downgrades or any other condition in which the load
NASON SAFETY CONTROLS
drives the engine.
The Nason (formerly Hawk) Safety Control System
provides protection from low lubricating oil pressure and
Operate at partial throttle in continuous duty situations to
excessively high coolant temperature of preset values.
When either is exceeded, the controls disrupt the
approximately 15 percent below governed speed.
electrical circuit to the fuel solenoid shutdown valve and
shuts down the engine. The oil pressure safety control is
OIL TEMPERATURE GAUGE
mounted directly in the main oil gallery. The temperature
safety control mounts directly into the water manifold.
The oil temperature gauge normally should read between
180 deg. F [82 deg. C] and 225 deg. F [116 deg. C] for
During cranking of engine a permissive start switch is
best lubrication. Any sudden increase in oil temperature
used to bypass the low lubricating oil pressure safety
which is not caused by load increase is a warning of
possible mechanical failure and should be investigated at
Actual cranking is accomplished by use of a push button
type starting switch wired into the cranking circuit. See
wiring diagram Fig's. 151, A and B.
WATER TEMPERATURE GAUGE
A water temperature of 165 deg. to 195 deg. F [74 deg.
to 91 deg. C] is the best assurance that cylinder liners
are heated to the proper .temperature to support good
combustion and that working parts of the engine have
expanded evenly to the most favorable oil clearances.
Overheating problems require mechanical correction. It
may be caused by loose water pump belts, a clogged
cooling system or heat exchanger, or insufficient radiator
capacity. Report cases of overheating to the
maintenance department for correction; 200 deg. F
[93.3 deg. Cl maximum engine coolant temperature
should not be exceeded.
OIL PRESSURE GAUGE
The oil pressure gauge indicates any drop in lubricating
oil supply or mechanical malfunction in the lubricating oil
system. The operator should note loss of oil pressure
immediately and shut down the engine before the
bearings are ruined. Individual engines may vary from
above normal pressures. Observe and record pressures