MAINTENANCE OF ENGINE PREHEAT ASSEMBLY
GENERAL. The engine preheat system maintains
the engine in preheated, ready-to-start condition in
ambient temperatures from 125°F (52°C) to 32°F (0°C),
and with the optional housing kit installed, to -25°F
(-32°C). The system operates from an external 115V
AC power source. It consists of an electrically operated,
thermostatically controlled engine coolant heater, piping
and valves. Coolant temperature is thermostatically
controlled at 100 to 120°F (47 to 49°C). The engine
preheat assembly is located in the base assembly under
the engine. See figure 8-1.
HEATING ELEMENT (see figure 8-2)
Replacement. Remove cover (4) to gain
access to heating element terminations. Tag
and disconnect wires. Unscrew heating
element (6) from EB tank (23). When installing
new element add sealing compound MIL-5-
15204C to pipe threads.
Test. Heating element is actually comprised of
two separate 120V, 2200 watt elements.
Utilizing a 120V AC 20 AMP power source,
energize each element in turn to verify that
each element current draw is approximately
18.5 AMPS. See figure 8-3. If any element
does not have proper current draw, replace
THERMOSTAT (see figure 8-2)
Replacement. Remove cap (8) and grommet
(10) from cap (11) to gain access to sensing
unit (13) terminations. Tag and remove wires
from thermostat. Remove thermostat sensing
unit (13). Immerse sensing unit into hot water.
As hot water temperature reaches 120°F,
sensing element contacts shall open (infinite
ohms reading). As water temperature cools to
100°F, sensing element shall reclose (0 ohms
reading). See figure 8-4.