TM5-6115-593-34NAVFAC P-8-631-34TO-35C2-3-463-2CHAPTER 8MAINTENANCE OF ENGINE PREHEAT ASSEMBLY8-1.GENERAL. The engine preheat system maintainsthe engine in preheated, ready-to-start condition inambient temperatures from 125°F (52°C) to 32°F (0°C),and with the optional housing kit installed, to -25°F(-32°C). The system operates from an external 115VAC power source. It consists of an electrically operated,thermostatically controlled engine coolant heater, pipingand valves. Coolant temperature is thermostaticallycontrolled at 100 to 120°F (47 to 49°C). The enginepreheat assembly is located in the base assembly underthe engine. See figure 8-1.8-2.HEATING ELEMENT (see figure 8-2)a.Replacement. Remove cover (4) to gainaccess to heating element terminations. Tagand disconnect wires. Unscrew heatingelement (6) from EB tank (23). When installingnew element add sealing compound MIL-5-15204C to pipe threads.b.Test. Heating element is actually comprised oftwo separate 120V, 2200 watt elements.Utilizing a 120V AC 20 AMP power source,energize each element in turn to verify thateach element current draw is approximately18.5 AMPS. See figure 8-3. If any elementdoes not have proper current draw, replaceentire element.8-3.THERMOSTAT (see figure 8-2)a.Replacement. Remove cap (8) and grommet(10) from cap (11) to gain access to sensingunit (13) terminations. Tag and remove wiresfrom thermostat. Remove thermostat sensingunit (13). Immerse sensing unit into hot water.As hot water temperature reaches 120°F,sensing element contacts shall open (infiniteohms reading). As water temperature cools to100°F, sensing element shall reclose (0 ohmsreading). See figure 8-4.8-1
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