Fuel Heater: Description and Operation

Fig 4 Fuel Heater And Temperature Sensor Location:

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

DESCRIPTION
The heater assembly is equipped with a built-in sensor (thermostat) that senses fuel temperature.

OPERATION
When the temperature is below 40 degrees F, the built-in sensor allows current to flow to the built-in heater element warming the fuel. When the temperature is above 80 degrees F, the sensor stops current flow to the heater element. Voltage to operate the fuel heater is supplied from the ignition switch and through the fuel heater relay. The built-in heater element operates on 12 volts, 300 watts at 0 degrees F. As temperature increases, power requirements decrease

A minimum of 7 volts is required to operate the fuel heater. The resistance value of the heater element is less than 1 ohm (cold) and up to 1000 ohms warm.

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.

NOTE: The fuel heater and fuel heater relay are not controlled by the powertrain control module (PCM).

The fuel heater assembly contains a pre-filter to prevent contaminants from entering the fuel transfer pump.