MIL-T-62735 Trucks And Truck Tractors: Modified Commercial, General Specification ForThis specification covers general requirements for the classes, models and types of modified commercial trucks indicated in the specification title above and in 1.2 below. This specification is intended only as a document to be referenced in detail specification sheets that must, as a minimum, cover detailed truck body requirements and specify the model and class required from table I.

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MIL-T-62735

3.5.24.3  Heaters. Heaters shall be as follows:

(a)   The engine block or the lower coolant inlet hose shall have a coolant heater,

1,000-watt (W) minimum rating on trucks up to class 22 and 1,500-watt minimum rating for larger trucks.  An engine thermostat with an operating range of 77°C to

90°C (170°F to 195°F) shall be installed.

(b)   The oil pan shall have a heater of the permanent external surface mount, permanent

in-pan mount, or immersion type that meets the following requirements: (1)   Not less than 16 W/L (16 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.

(c)   Diesel engines shall have a fuel warmer to prevent clogging of fuel filters due to wax

crystallization in the fuel.  The fuel warmer shall use engine coolant to transfer sufficient heat to the diesel fuel to heat it from an inlet temperature of -40° (-40°F) to an outlet temperature of -13°C (+9°F), with a fuel flow rate not less than the maximum fuel demand of the engine fuel system.  The system shall include a

coolant shutoff valve for the coolant inlet side of the fuel warmer unit.  The system shall not cause heating of the fuel above 27°C (80°F) under any possible condition.

(d)   Diesel engines shall have an in-tank fuel warmer.  The warmer shall use engine coolant to transfer heat to the fuel in one fuel tank.  The warmer shall not cause

heating of any fuel above 27°C (80°F) under any possible condition, shall not disable or cause elimination of the fuel gage sending unit and shall not violate 3.1.1

or any Federal Motor Carrier Safety Regulation.  A coolant shut off valve shall be included.  The units required by 3.5.24.2(c) and (d) may be combined.

3.5.25  Fuel fired engine preheater.  When specified (see 6.2), for diesel engine driven vehicles, the vehicles shall have a diesel fuel fired engine water heater to preheat the engine and the fuel.  The heater shall include a timer, a thermostat, a circulating pump and connection into the engine coolant system.  The heater shall be capable of starting and operating at -51°C

(-60°F).  The heater shall heat the engine from -51°C (-50°F) to 4  C (+40°F) in not more than

1 hour.

3.5.25.1  Preheater controls and indicator light.  The system shall have a starter on/off switch, accessible to the seated driver.  The system shall include fuel warmers in accordance

with 3.5.24.2(c) and (d).  The system shall be have an indicator light, visible to the seated driver, to indicate that the preheater is operating.  The purpose of the switch and light shall be indicated

by marking in accordance with 3.10.5.

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