TM55-2840-251-23
Section III PRINCIPLES OF OPERATION (Continued)
1-12 LUBRICATION SYSTEM (Cont)
Oil-to-Fuel Heater
The oil-to-fuel heater is self-contained and is secured to
flange G on the accessory gearbox. It functions as a
heat
exchanger,
utilizing
heat
from
the
engine
lubricating system to pre-heat fuel in the engine fuel
system. The heater is only effective during periods
when the engine is running and will automatically
maintain the outlet fuel within a 70 degree F to 90
degree F (20 degree C to 32 degree C) temperature
range. The system incorporates a two-pass engine oil
circuit and two-pass fuel circuit each at right angles to
the other (. refer to figure). A temperature control valve
regulates the fuel temperature either by permitting oil
through the heater core, or by-passing it through the
valve back to the engine oil tank through an external
line.
Hot engine oil enters the oil circuit through the oil inlet
port of the heater under engine pressure. If the outlet
fuel temperature is less than the ball valve setting the
vernatherm plunger will retract and the ball will seal the
by-pass port, forcing the engine oil to circulate through
the walls of the heat exchanger to warm the engine fuel.
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