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14black 03-15-2019 10:44 AM

Head Scratcher
I've been trying to solve this problem for a couple of months.

Background : 2014 F350 6.7, auto trans. Deleted in 2016. 420,000 miles currently on truck. Truck does not use oil between changes. Oil sampled and sent to lab every oil change (12,000 miles). Report stated all wear metals are good. No glycol or fuel in oil. The egr is still on truck but bypassed. The cooling lines are still attached.

Problem : Since the delete the truck has performed great, no problems. A month ago the cooling fan cycles on and off all the time. My mechanic has plugged in the IDS to check things out. Any system that would command the fan to engage are reading within parameters. The fan hub was replaced, no change. It will cycle at idle or at speed. The truck does not overheat at speed.

Took the tune out and reinstalled in case it got corrupted, no change. Even my mechanic is stumped and he is a Ford trained tech and works a Ford dealer. I consider him top notch. All sensors have been checked and are working properly.

I am looking for a fresh set of eyes and to see if anyone out there has experienced this or heard of it. If you have ANY ideas, please share. I use this truck in a commercial hauling business and getting kind of tired of the crappy fuel mileage this problem creates.

Thanks in advance for any ideas.


djousma 03-15-2019 01:08 PM

Might just be time to replace the thermostat?

14black 03-16-2019 12:17 AM


Thanks for the come back.Replaced thermostat at 302,911 miles. Not saying it hasn't went bad again.

jimmy 03-16-2019 09:31 AM

Did the fan cycle while the PIDS for temps from those things were monitored? Chafed wires are common on super duties, well any vehicle with wires used in dirty environment--SDs have no exclusive on chafed wires, and sensor signal wires getting resistive connections to ground look like high temps. The temp sensors have resistance to ground that gets less resistance as temp goes up. A wire with worn insulation that gets pulled against some piece of engine or chassis metal will often not be a 0 ohm reading but will be 100, 250, 500 ohms depending on the dirt and oil and cleanliness of contacted metal. There is no fault code set for these problems until they get to be a direct short that makes the input signal go out of the plausible range.

14black 03-17-2019 01:50 AM

Hi Jimmy

Yes, the fan cycled while being monitored. The ids showed fan rpm increasing while everything that would turn the fan on remained within normal ranges.

Thank You for the response .


jimmy 03-18-2019 12:23 AM

Next is unplug Viscotronic fan clutch wire and see if the cycling occurs with no control signal.

ford_doctor 03-18-2019 07:57 AM

Monitor your A/C pressure along with your A/C request parameters. A fault with the pressure sensor/circuits will cause the fan to come on. If you do find the A/C pressure going high and find no obvious fault with the sensor consider the thermostatic expansion valve. If it sticks causing high pressure the fan will come on. My experience with TXV's on these trucks is that they can stick for no apparent reason. Most of the time they can be un-stuck simply by recovering the refrigerant and then evacuating and recharging though debris from a failing compressor should not be ruled out... neither should a malfunctioning transmission fluid temperature sensor. The A/C scenario will not leave a code, the TFT should. Keep that in mind.


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