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Page Title:
Power plant heaters and fuel warmer |
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|  MIL-T-62097C
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 Power plant heaters and fuel warmer. When specified (see 6.2), a coolant heater,
an engine oil heater, and fuel warmers (diesel engine driven vehicles only) shall be provided.
The 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 for grounding the vehicle. A
three-wire connecting cable, not leas than 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, 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). The electrical insulation of the connecting cable
shall withstand normal operating stresses in low ambient air temperatures (down to -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 assembly shall be provided. Heaters and fuel warmers shall be furnished as
follows:
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(a) A coolant heater, 1000-watt minimum rating, shall be installed in the engine block or
in the lower coolant inlet hose. An engine thermostat with an operating range of
170F to 195F shall be installed.
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(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 15 watts per quart heating capacity
(2) Not more than 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.
*
(c) An in-line fuel warmer or preheater unit shall be provided on diesel engine driven
vehicles to prevent clogging of fuel filters due to wax crystallization in the fuel. The
unit shall use engine coolant to transfer sufficient heat to the diesel fuel to heat it
from an inlet temperature of -40F to an outlet temperature of +9F, with a flow rate
not less than the maximum fuel demand of the engine fuel system. A coolant shutoff
valve shall be provided for the coolant inlet side of the fuel warmer unit. The unit
shall not cause heating of the fuel above 80F under any possible condition.
*
(d) An in-tank fuel warmer or preheater unit shall be provided on diesel engine driven
vehicles. The unit shall use engine coolant to transfer heat to the fuel in one fuel
tank. The warmer shall not cause heating of any fuel above 80F under any possible
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