2011 F150 5.0 with 150K miles. When driving 2,000 RPM or above regardless of speed, the temp gauge will slowly rise to Hot and the high temp warning will display. Stop truck and the gauge immediately goes to normal.
Below 2,000 RPM there is no issue.
No leaks, fans are working, Do my own maintenance. All hoses, thermostat, water pump, and belts were changed 6 months ago
for preventative maintenance.
It seems to me a belt slipping or water pump issue, however I am wondering if anyone else has had this problem?

 

My first thoughts would be a water pump failing or leaves/crud stuck between the radiator and condensor slowing air flow ( seen the 2nd many times actually)

 

Make sure the thermostat isn't installed backwards. Also I would do a flush on the entire system. Maybe you left a rag in one of the inlets when you did all that work? Could also be air in the system?

 

Did you replace the Idler/tensioner pulley?

 

Start simple. Radiator clean? Coolant full? Air in system?

Verified temp increase with temp gun?

Id replace the thermostat again with an oem one. They can be bad.

Next i'd look at the water pump.

 

Good advice ^^^

No need to spend money unless you need to.

 

This system seems to be temperamental about coolant level and thermostats. It's easy to be low on coolant, and it's common for non-OEM thermostats to not work. Even new.

 

Well, I did all easy stuff, cleaned radiator and changed thermostat, again. No help, so I borrowed my son’s Edge Insight Cts that plugs into the OBD II which allowed me to monitor all temps etc. Temp sensor indeed reading high temp, so to check sensor, let truck sit over night to equilibrate trans temp, engine temp, and ambient temp. All were within a degree or 2.
Thinking back, when I replaced water pump, it was a Gates and I believe it had a plastic impeller. Ordered an AC Delco from Rock Auto with metal impeller. Will try that and see

 

Sounds like a good next step, I've never seen a plastic impeller before. I've seen aluminum and cast iron. Maybe with the heat it softened and no longer spinning correctly.

 

Motorcraft/Ford from the factory is plastic impeller.