Engine Temp gauge has large temperature swings in seconds between 205 and 226 degrees

[st381183]

2018 Expedition XLT Max. I just recovered from a tranmission overfill / overheat issue thanks to negligent dealer service. Now the electronic engine temp gauge in the cluster swings from 226 degrees on the high end to 205 degrees, spiking lower sometimes to 198 degrees on the low end within seconds. Then the temp sits at 210-215, then the temp starts swinging again. Highway and street. Seems to me engine temp should be steady. I've never encountered this issue. I have been told my battery is not good, but all systems are working and it starts. Could this be a battery going bad issue or a thermostat issue, or does the engine temp gauge do that and I just haven't noticed before? So far it hasn't gone over 226 degrees. Any help would be appreciated in diagnosing the issue.

 

[JasonH]

Was any of the cooling system serviced recently or is this a new issue? Could be air in the cooling system.

 

[st381183]

Not serviced directly... The transmission overheated due to being overfilled which cause an engine temp spike. I wonder if the coolant boiled and produced air pockets….I will try to bleed any air out this evening. Still open to any other ideas. Thanks

 

[JasonH]

My recollection is that on the 4th gens the transmission heat exchanger transfers heat to a coolant loop. Ford Tech Makuloco has a good video on bleeding air from the system. I used it when I changed my water pump. I would start there, as it's relatively easy.

Ford Quick Tips #69: The Trick to Purging Air From Your Cooling System

Come along as we show you how to purge air from your engine cooling system.Vacuum Refill Tool-http://amzn.to/2iJT0GIVacuum Fill Tool Demonstration-https://ww...

youtu.be

Apart from that, the coolant system should be pressure tested before you start swapping parts.

 

[Going_Going_Gone]

If you're going to be going into your cooling system, you might want to consider replacing your thermostat with the latest version RT-1252
ford-quietly-redesigned-the-thermostat-in-2022-replace-it.53242

 

[LokiWolf]

Temp swings, like you thought are either air pockets like was said, or the Thermostat needs replacing, and you should use the new part number like was mentioned.

 

[BP 09]

If it’s changing temps in seconds like you said, definitely air pockets.

With a good thermostat and healthy water pump on a stock gen 2, I have seen temps go to around 220, the radiator fan then kicks on and drops them to 205 or so. Then eventually they work their way back up. But this happens over minutes not seconds.

Now I’ve got a 170 t stat. Have yet to see anything over 195

 

[DavidCola]

2018 Expedition XLT Max. I just recovered from a tranmission overfill / overheat issue thanks to negligent dealer service. Now the electronic engine temp gauge in the cluster swings from 226 degrees on the high end to 205 degrees, spiking lower sometimes to 198 degrees on the low end within seconds. Then the temp sits at 210-215, then the temp starts swinging again. Highway and street. Seems to me engine temp should be steady. I've never encountered this issue. I have been told my battery is not good, but all systems are working and it starts. Could this be a battery going bad issue or a thermostat issue, or does the engine temp gauge do that and I just haven't noticed before? So far it hasn't gone over 226 degrees. Any help would be appreciated in diagnosing the issue.

I had this same problem after some cooling hose replacement. I heard that there maybe air in the system to "this is normal". Chased my tail for a while in finding a solution. It is well documented on line, but not recognized by dealers that the thermostats go bad. Ford redesigned the thermostat. I replaced mine and have not had any problems, including 100+ days in SC.

 

[Wangle]

Yes, replace your thermostat. Pretty easy job. The new Motorcraft design is said to be 190°, but the Celsius reading stamped on the thermostat indicates it is still 195°. Even so I’ve seen a more constant temperature.