COLD WEATHER STARTING
LEARNING OBJECTIVE: Identify the
different types of cold weather starting aids.
Diesel fuel evaporates much slower than gasoline
and requires more heat to cause combustion in the
cylinder of the engine. For this reason, preheating
devices and starting aids are used on diesel engines.
These devices and starting aids either heat the air before
it is drawn into the cylinder or allow combustion at a
lower temperature than during normal engine
The purpose of a glow plug is to beat up the air that
is drawn into the precombustion chamber to assist
starting, especially in cold weather. Glow plugs are
common on precombustion chamber engines, but not
on direct injection diesels because they use shaped
piston crowns that produce a very effective turbulence
to the air in the cylinder. Direct injection engines also
have less immediate heat loss to the surrounding
cylinder area than in a precombustion engine and
generally have a higher injection spray-in pressure.
A glow plug is used for each cylinder located just
below the injection nozzle and threaded into the
cylinder head (fig. 5-43). The inner tip of the glow plug
extends into the precombustion chamber. The glow
plugs may be turned on using the ignition switch with
N O T E
When troubleshooting or repairing these
units, you should consult the manufacturer's
Figure 5-43.Typcial diesel glow plug.
the length of time being controlled from an electronic
module. On some older vehicles and construction
equipment, glow plugs are operated by manually
depressing a switch or button for 15 to 30 seconds.
During colder weather, the system may have to be
cycled more than once to start the engine.
Glow plugs are not complicated and are easy to test.
Disconnect the wire going to the glow plug and use a
multimeter to read the ohms resistance of the glow plug.
Specifications for different glow plugs vary according
to the manufacturer. Be sure and check the
manufacturers service manual for the correct ohms
MANIFOLD FLAME HEATER
The manifold flame heater (fig. 5-44) is another
type of cold starting system found on diesel engines.
This system is composed of a housing, spark plug, flow
control nozzle, and two solenoid control valves. This
system operates as follows:
The flame heater ignition unit energizes the
The nozzle sprays fuel under pressure into the
intake manifold assembly.
The fuel vapor is ignited by the spark plug and
burns in the intake manifold. The heat from this
fire warms the air before it enters the
The flame fuel pump assembly is a rotary type,
driven by an enclosed electric motor. The fuel pump
receives fuel from the vehicle fuel tank through the
supply pump of the vehicle and delivers it to the spray
nozzle. The on/off switch, located on the instrument
panel, energizes the pump.
The intake manifold flame heater system has a filter
to remove impurities from the fuel before it reaches the
The two fuel solenoid valves are energized (open)
whenever the flame heater system is activated. The
valves ensure that fuel is delivered only when the
system is operating. These valves stop the flow of fuel
the instant that the engine or heater is shut down.