Hi

2018 F150 3.5l ecoboost screw

Towing my travel trailer (about 5000lbs) and coolant temperature gauge fluctuates. Goes to about 2/3 towards hot then comes back down. Does this repeatedly and constantly while towing. Never overheats or gives warnings. When not towing rad fans on high a lot. Never used to do this. Any ideas what might be going on? Oh and I haven't had any work done on it recently.

Thank you

 

Likely the Sensor, plug-up or Harness is faulty or intermittent.
If the PCM gets a signal that temp is too high, it turns the Fans on.
Good luck.

 

I used to see this when I had the fifth wheel though not to that extreme. Using an OBD II Bluetooth module and Torque pro on my phone to monitor the temperature I noted normal running was 222-3 deg. it would often rise nearing 240 then drop down about 12 - 15 degrees. My thought was a faulty thermostat. I think OEM is 195 deg but I was always running way hotter than that. I found a MOTORCRAFT 180 deg. replacement to install and the temperatures smoothed out. Now the high temps are at 222 deg and the normal running is 204 deg. without any of the surge. I never checked it but I do think the original was faulty. On reflection a 188 Deg replacement thermostat would be a better choice and maybe someday I'll change it.