Stock filter housing heater

[DP]

What is the logic and timing for the heater in the stock filter housing? I know that in the service manual it says that when testing to only supply power to the heater for 30 seconds at a time. When is this thing on and what determines its cycling?
Thanks.

[diesel65]

The fuel heater turns on when the temperature of the fuel coming in is below 58 degrees and turns off when the temp goes over 75 degrees.

[Hubert]

diesel65 don't take this the wrong way but where did you learn that? I have read a few other things and thought I have read it was more like below 40, 43, or 48 F can't remember exactly. My understanding is it comes on if below cuts off if above. No. 2 fuel should be fine until low 40's before it clouds then cooler still before other nasties develop.

Thinking from a controls standpoint your on off points are better than it cycling on off if its near set point but if it does pulse or cylce on and off then a one sided set point would work ok. The placement of the manager being in the valley of engine affords it some heat that will help reduce the demand for the heater once stable operation is reached.

This is first I have read of it cycling on off or testing with a duty cylce. I guess its a safety thing wouldn't want a burned out element shorting or other mixed with fuel. Or maybe its to keep wiring cool and safer??? Might be once the element is hot enough to warm fuel it takes so long for new fuel to cool it back down and no since continuously heating warm fuel.

[DmaxMaverick]

Early models are thermistor regulated (like later glow plugs), later models are PCM controlled. I don't remember the exact on/off temps, but what diesel65 posted sounds about right.

Although #2 flows above freezing, it flows better when warmer. As it approaches the cloud point (well above the gel point), its viscosity increases significantly. 70° is ideal. Once the engine runs for a while, the return cycle keeps the fuel inlet temp warmer (to a point, depending on the ambient temp). The filter heater will work more often as the ambient temp drops, and the fuel in the tank and lines shed more heat.

[More Power]

The fuel heater is energized when the ignition key is on and the temperature is 20 degrees F or below. This 20 degree setting was not chosen arbitrarily. 20 degrees F is the gell point for summer #2 diesel.

The 30 second warning may apply when testing the heater off the truck and without it being submerged in fuel. :)

Jim

[diesel65]

Came from the GM 6.5L Turbo Diesel Engine training manual issue #16015.12-2, November 1992, page 8-34.
Page 7-21 gives you the diagnostic procedure using heat, then using ice with the values I previously mentioned. It tells you after you cooled down the heater, coat the heater with fuel then connect for 30 seconds and observe if element is heating.
I used to go to the GM training center in Tarrytown NY when I worked for Pontiac, While there, if I ever needed information and a book was available, all I had to do was ask.

[Hubert]

Thanks diesel65 for suppling source I had to look all over the place but remembered something like this......

I think "cloud point" is 40-43F depending on where you google and would be highly dependant on fuel blend additives etc so could vary still.

I am just putting this out there for info and am not saying all years or even this info is totally correct but for a '97 According to Alldatadiy.com

Clipped....
"Fuel Heater
The fuel heater operates when the temperature of fuel at the inlet of the filter housing is cold enough to possibly cause waxing that could restrict flow to the injection pump. A control circuit inside the fuel heater completes the circuit for the heater element when it senses a temperature below 8°C (46°F)."

Again for a '97

Now at the IP optical sensor there is a thermistor that measures fuel temp also and for that location its different than at fuel manager and my helm book says this ...

Fuel temp measurement range is like -18F to 285F.
Also read a DTC will set if fuel is measured below 64F iirc measured at optical sensor after more than 8 minutes with truck running normally condition measured more than 2 seconds.
(ECT above 160F)

And Fuel temp greater than 215F condition met for 2 seconds (ECT min 160F stable operation).

From the above 64F is pretty high for minimum fuel temp and either the IP and or location adds some appreciable heat or the heater does stay on til 64F???