Dodge RAM TRUCK 1500 1995 Service Manual page 1185

GENERAL DIAGNOSIS—DIESEL ENGINE 14 -113
Fig, 10 installing Special Tools
the fuel filter/water separator. Excess water can be
drained. Refer to Fuel Filter/Water Separator in the
Diesel Engine—Component Removal/Installation sec­
tion of this group for water draining procedures.
If excess water gathers in the filter/separator in a
short period of time, the fuel tank must be removed,
drained and cleaned.
For removal and installation procedures, refer to
the Diesel Engine—Component Removal/Installation
section of this group.
FUEL HEATER TEST
The fuel heater is used to prevent diesel fuel from
waxing during cold weather operation.
The fuel heater element, fuel heater relay and
fuel heater temperature sensor are not con­
trolled by the powertrain control module
(PCM).
A malfunctioning fuel heater can cause a wax
build-up in the fuel filter/water separator. Wax
build-up in the filter/separator can cause engine
starting problems and prevent the engine from rev­
ving up. It can also cause blue or white fog-like ex­
haust. If the heater is not operating in cold
temperatures, the engine may not operate due to fuel
waxing.
The fuel heater is located on the left side of the en­
gine above the starter motor (Fig. 11).
The heater assembly is equipped with a built-in
fuel temperature sensor (thermostat) (Figs. 11 or 12)
that senses fuel temperature. When the fuel temper­
ature is below 40 degrees F, the sensor allows cur­
rent to flow to the built-in heater element to warm
FUEL TEMPERATURE SENSOR
Fig. 12 Fuel Heater Assembly
the fuel. When the fuel temperature is above 80 de­
grees F, the sensor stops current flow to the heater
element (circuit is open).
Voltage to operate the fuel heater element is sup­
plied from the ignition switch, through the fuel
heater relay (Fig. 13) (also refer to Fuel Heater Re­
lay), to the fuel temperature sensor and on to the
fuel heater element.
The built-in heater element operates on 12 volts,
300 watts at 0 degrees F. As temperature increases,
power requirements decrease.
The fuel heater assembly contains a pre-filter (Fig.
12) to prevent contaminants from entering the fuel
transfer pump.