MIL-T-62246 Truck, Dump, Street Maintenance, Diesel And Gasoline Engine Driven, 21,000 Pounds Gvw, 4X2, CommericalThis specification covers diesel and gasoline engine driven, four-wheel, two-rear-wheel drive dump trucks equipped with a material sprayer, an auxiliary engine driven air compressor, and a vibrating roller for use in street maintenance. Vehicles shall have a minimum gross vehicle weight GVW of 21,000 pounds for normal operating conditions. Vehicles procured under this specification are commercial items which shall be warranted by the manufacturer as specified in acquisition documents.

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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 60°F) 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 170°F to

195°F shall be installed

(b)    An immersion type engine oil heater, 300-watt minimum rating, with 170°F to

195°F 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 10°F during vehicle exposure in ambient air temperatures as low as minus 60°F, and shall include a thermostat to limit the temperature of the electrolyte to not more than 80°F

(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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