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Page Title:
Power plant heaters and fuel warmers |
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|  MIL-T-62491C
3.4.1.6 Coolant temperature control. Thermostatic control of engine coolant temperature
shall be provided. On diesel engine driven vehicles, the control shall include complete thermostatic
control of all coolant flow through the radiator.
3.4.1.7 Fan clutch. A fan clutch shall be provided. The fan clutch shall reduce the fan speed
automatically when the fan is not required for engine cooling. The fan clutch shall be asbestos
free.
3.4.1.8 Silicone rubber hoses. When specified (see 6.2), except for class 10 wreckers,
silicone rubber radiator and heater hoses shall be furnished.
* 3.4.1.9 Power plant heaters and fuel warmers. When specified (see 6.2), a coolant heater, an
engine oil heater and fuel warmers (diesel engine driven vehicles only) shall be provided. Heaters
shall operate on 110-volt alternating current (ac), and shall be wired through a junction block,
including a fuse or circuit breaker, to a single three-pronged (male), weatherproof slave receptacle
for receiving external power and grounding the vehicle. The receptacle shall be located on the
streetside of the vehicle, as near the cab door as practicable. A three-wire connecting cable, not
less than 7600 mm (25 feet) long and of adequate line capacity to supply power for all heater units
simultaneously, shall be furnished. The connecting cable shall include a matching female
connector at the vehicle end and a standard, weatherproof, three-pronged (two power plus one
ground) male connector at the other end. Electrical apparatus shall conform to Federal Motor
Carrier Safety Regulation 393.77(c)(7). Electrical insulation of connecting cable shall withstand
normal operating stresses in low ambient air temperatures (down to -51C (-60F)) without
cracking or loss of dielectric capacity. All heater lead wires shall be installed without interfering
with vehicle component operation, and without loose excess wire. Provisions for stowage of the
cable shall be provided in the vehicle cab. Heaters and fuel warmers shall be furnished as follows:
(a) A coolant heater, 1000-watt (W) minimum rating, shall be installed in the engine block or
lower coolant inlet hose. An engine thermostat with an operating range of 77C (170F)
to 90C (195F) shall be installed.
*
(b) An oil pan heater of the permanent external surface mount, permanent in-pan mount, or
immersion type that meets the following requirements, shall be installed:
*
(1) Not less than 16 W/L (15 watts per quart) heating capacity
(2) Not more than 2.8 watts per square centimeter (W/cm2) (18 watts per square inch)
heating capacity
(3) Thermal balance design or thermostat control providing for uninterrupted operation
(4) Provision for mounting below minimum service oil level.
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