To keep diesel engines in peak operating
condition, the operator must give careful attention to
the following factors-prestart inspection, starting the
diesel, securing the diesel, and operator maintenance.
Before a diesel can be started, the operator must
perform a prestart inspection to ensure the engine is
ready for operation. The specific inspection routine
varies somewhat according to each engine. The basic
procedure, however, requires the operator to inspect
the engine for a sufficient supply of fuel oil, lube oil,
and cooling water. The operator must also be alert for
any leakage of these fluids. When replenishment of
cooling water is necessary for the radiator, use clean or
soft water to keep the engine water jackets and coolant
circulating system free of sediment. If the engine is
still hot from previous operation, do not add large
amounts of cold water.
Sudden cooling can crack
cylinders or cylinder heads and may cause unequal
contraction of the structural and working parts and lead
to seizing of the pistons. When topping off batteries,
use distilled water.
Accessories and drives should be inspected for
loose connections and mountings. If the diesel starting
system is battery equipped, check the batteries for
cracks and leaks, and ensure the battery cables and vent
caps are clean and secure.
As a safety precaution, inspect the fire extin-
guisher for ease of removal, full charge, security, and
cleanliness of valves and nozzles before starting the
Diesel engines rely on some external source of
power for starting. The starting mechanism may be an
electric motor, an auxiliary gasoline engine,
compressed air, or even a hand-cranking mechanism.
Whatever system is used, the starter forces the pistons
to reciprocate and compresses air drawn into the
cylinders. When sufficient compression has been
developed with the aid of the starter, the temperature of
the air in the cylinders will be high enough to ignite the
injected diesel fuel. Thus internal combustion takes
place and the engine begins to crank under its own
power. Once the engine has been started, the actions
the operator must take are as follows:
1. Throttle the engine to normal (fast idle) warm-
up speed. The diesel should not be permitted to slow
idle for any appreciable length of time because this
causes the engine-driven blower to deliver an
insufficient amount of air for complete combustion.
This condition results in partially burned fuel oil,
forming heavy carbon deposits that foul the valves, the
piston rings, and the exhaust system.
2. Immediately check the lube oil pressure gauge.
If the gauge does not indicate positive and sufficient
lube oil pressure within 30 seconds, stop the engine
immediately and report the difficulty to the proper
3. Observe the temperature gauge during the
warm-up period. The engine must not be placed under
load until it reaches the proper warm-up temperature.
Placing a cold engine under full load can result in
serious damage to the engine because of poor
lubrication at low temperature and uneven rates of
While the engine is in operation, other inspections
and checks are required, such as checking of lube oil
and fuel oil levels, filters and strainers, accessories and
drives, and engine operating temperatures and
pressures. Normally, the operator records the results
of these inspections in an operating log.
When the diesel is secured, if the engine
installation permits, let the engine low idle without
load for a short time before stopping to allow for a
gradual reduction of engine temperature. Once the
diesel has been shut down, the standby lube oil pump
should be kept in operation for a short time to allow the
lube oil to further cool the engine. The cooling water
should also be kept circulating for 15 to 30 minutes to
bring the working parts to a low temperature without
danger of distortion from one part cooling faster than
While the engine is cooling, the operator must
check to determine the need for adjustment, for repair,
and for replacement or renewal of parts. The required
actions are as follows:
Check the fuel, the oil, and the water as in the
Check the engine instruments or the gauges for
Check the accessories and the drives as in the
Inspect the air cleaners and the breather caps.
Inspect the fuel filters.
Inspect the engine controls and the linkage.
Inspect the batteries as in the prestart inspection.
Inspect all electrical wiring, insulation, and
security of connections.