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Fluctuating Temperature Gauge Issues

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Old Jan 15, 2022 | 05:05 PM
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Default Fluctuating Temperature Gauge Issues
I have a 2016 F150 3.5L Ecoboost that keeps having issues with fluctuating engine temp. I’ve had the thermostat, water pump, temperature sensor all replaced, but keep having the same issue.

I did notice that when the radiator fan kicks on high, this is when the temperature fluctuates. Could this be because of an erratic/bad radiator fan?
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Old Jan 15, 2022 | 05:33 PM
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Originally Posted by dluk21
I have a 2016 F150 3.5L Ecoboost that keeps having issues with fluctuating engine temp. I’ve had the thermostat, water pump, temperature sensor all replaced, but keep having the same issue.

I did notice that when the radiator fan kicks on high, this is when the temperature fluctuates. Could this be because of an erratic/bad radiator fan?
Could be a bad CHT sensor. They are not very expensive. The CHT (Cylinder Head Temperature) sensor provides the engine temperature that the PCM uses to control the fans and the IPC uses to display an inferred coolant temperature.
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Old Jan 15, 2022 | 05:48 PM
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Originally Posted by 52merc
Could be a bad CHT sensor. They are not very expensive. The CHT (Cylinder Head Temperature) sensor provides the engine temperature that the PCM uses to control the fans and the IPC uses to display an inferred coolant temperature.
I believe this is the sensor that I had replaced last. I didn’t have any issues for over 200 miles until I slowed down on an off-ramp getting off the highway. Then the fan kicked on high and temp started to go up.

Any other ideas?
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Old Jan 15, 2022 | 05:57 PM
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I would check for DTCs. Not all DTCs illuminate the CEL. FORScan or high-end diagnostic tool is best for checking DTCs.
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Old Jan 15, 2022 | 06:19 PM
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Originally Posted by 52merc
I would check for DTCs. Not all DTCs illuminate the CEL. FORScan or high-end diagnostic tool is best for checking DTCs.
Got it. Thanks for the help. I have a mid-tier code reader myself, but might have to try to get my hands on a high end one

All said and done in the recent months I’ve had those parts above replaced, as well as the plugs and boots.

May have to take it to a dealership to see what they can find out.
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Old Jan 15, 2022 | 06:40 PM
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Originally Posted by dluk21
I have a 2016 F150 3.5L Ecoboost that keeps having issues with fluctuating engine temp. I’ve had the thermostat, water pump, temperature sensor all replaced, but keep having the same issue.

I did notice that when the radiator fan kicks on high, this is when the temperature fluctuates. Could this be because of an erratic/bad radiator fan?
The real fast short answer is: Did you replace the thermostat with an QEM thermostat !!! If you used a duralast or a Orielly's (simply a non oem stat) replace e it with a OEM stat.....
Stated many times on other posts your fans will operate @ high speeds........... you must use a Ford Oem stat !!!
For canadians CTC stats will not work either....been there done that !!!
Last edited by maco; Jan 15, 2022 at 06:44 PM.
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Old Jan 15, 2022 | 07:35 PM
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Originally Posted by maco
The real fast short answer is: Did you replace the thermostat with an QEM thermostat !!! If you used a duralast or a Orielly's (simply a non oem stat) replace e it with a OEM stat.....
Stated many times on other posts your fans will operate @ high speeds........... you must use a Ford Oem stat !!!
For canadians CTC stats will not work either....been there done that !!!
Yes. I’ve replaced the thermostat with a non-oem thermostat (temp still fluctuated) and then an OEM one. Seemed to solve the issue at first, but eventually overheated again, leading to the CHT sensor replacement.
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Old Jan 25, 2022 | 08:02 AM
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Maybe this:

NHTSA ID Number: 10201612 Manufacturer Communication Number: TSB 21-2250 Summary Some 2015-2020 F-150, 2017-2020 Super Duty and 2018-2020 Expedition/Navigator vehicles may exhibit poor air conditioning (A/C) performance, loss of airflow and/or engine cooling fans running continuously from high A/C pressures. This concern may be from the evaporator freezing up due to the evaporator temperature sensor being biased. To correct the condition, follow the Service Procedure steps to replace the evaporator temperature sensor. ​​​​​​​
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