Fuel Heater: Description and Operation

Fig.3 Filter Housing (Early):

Fig.4 Filter Housing (Late):

The fuel heater assembly is located on the side of the fuel filter housing (Fig. 3) or (Fig. 4).

The heater/element assembly is equipped with a temperature sensor (thermostat) that senses fuel temperature. This sensor is attached to the fuel heater/element assembly.

The fuel heater is used to prevent diesel fuel from waxing during cold weather operation.

When the temperature is below 45 ± 8 degrees F, the temperature sensor allows current to flow to the heater element warming the fuel. When the temperature is above 75 ± 8 degrees F, the sensor stops current flow to the heater element.

Battery voltage to operate the fuel heater element is supplied from the ignition switch and through the fuel heater relay. Also refer to Fuel Heater Relay.

The fuel heater element and fuel heater relay are not computer controlled.
The heater element operates on 12 volts, 300 watts at 0 degrees F.



The fuel heater is used to prevent diesel fuel from waxing during cold weather operation.

NOTE: The fuel heater element, fuel heater relay and fuel heater temperature sensor are not controlled by the Engine Control Module (ECM), or 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 revving up. It can also cause blue or white fog-like exhaust. If the heater is not operating in cold temperatures, the engine may not operate due to fuel waxing.

The fuel heater assembly is located on the side of fuel filter housing.

The heater assembly is equipped with a built-in fuel temperature sensor (thermostat) that senses fuel temperature. When fuel temperature drops below 45 degrees ± 8 degrees F, the sensor allows current to flow to built-in heater element to warm fuel. When fuel temperature rises above 75 degrees ± 8 degrees F, the sensor stops current flow to heater element (circuit is open).

Voltage to operate fuel heater element is supplied from ignition switch, through fuel heater relay (also refer to Fuel Heater Relay), to fuel temperature sensor and on to fuel heater element.