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|  MIL-T-62246B(AT)
* 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 partial thermostatic
control of coolant flow through the radiator and thermostatically controlled radiator shutters or
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.
3.4.1.8 Power plant heaters and fuel warmer. When specified (see 6.2), a coolant heater, an
engine oil heater, and a fuel warmer (diesel engine driven vehicles only) shall be provided.
Unless otherwise specified (see 6.2), a battery heater shall be provided when power plant heaters
are specified. Heaters shall operate on 110-volt alternating current (ac), and shall be wired
through a junction block to a single three-pronged (male), weatherproof slave receptacle for
receiving external power and grounding the vehicle. A three-wire connecting cable, 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 the connecting cable shall withstand normal operating
stresses in low ambient air temperatures (down to minus 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 shall be furnished as follows:
(a) A coolant heater, 1500-watt minimum rating, shall be installed in the engine block
or lower coolant inlet hose. Engine thermostat with an operating range of 170F to
195F shall be installed
(b) An immersion type engine oil heater, 300-watt minimum rating, with 170F to
195F thermostat, shall be installed in the oil pan through any convenient opening
(c) A battery heater shall have a capacity adequate to maintain the battery electrolyte at
a temperature of not less than 10F during vehicle exposure in ambient air
temperatures as low as minus 60F, and shall include a thermostat to limit the
temperature of the electrolyte to not more than 80F
(d) For diesel engine driven vehicles, a fuel warmer or pre-heater shall be provided to
prevent clogging of fuel filters due to wax crystallization in the fuel. The fuel
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