2017 F150 2.7 sport 80,000
was driving the truck approx 20 mins, at a light got warning for "engine coolant over temperature" then I believe the truck went into "limp mode" because I could barely change lanes to pull to the side of the road. No noises, no fluids leaking, no smoke. Coolant still full. Had the truck sit a few hours, started the vehicle and instant warning again. Truck towed.

Thermostat was bad. CHANGED. Replaced radiator cap. Bled system. Truck ran for about 8-10 mins, same warning, and now there is no pressure/flow through the hoses.

Thermostat sensor? Hose clog? Water pump? Trying to see if there is hopefully a simple fix before trying the radiator/blown head...

Most information I have found with this problem all indicate when the truck is towing... I was not towing. Truck does idle a lot.

 

Are you absolutely sure when you refilled the cooling system you purged all of the air?

 

How are you bleeding the system? Did you use a vacuum fill tool?

 

What brand T Stat did you use?

 

This is where an OBD adapter and apps like torque are nice. Then you could see the coolant temp sensors output on a cold motor. Getting the overheat code instantly on startup seems quite suspect to either the sensor its wiring.

 

Water pump?

 

Check the temperature sensor. Instant overheat after sitting a while like that doesn’t make sense.

 

I had VERY same things happen to me in first paragraph (including tow). 2.7 uses two sensors for coolant temp - Engine Coolant Temp (ECT) and Cylinder Head Temp (CHT). CHT seems to be primary. From the WSM "Closed Loop Mode

Stage 1 of the strategy commences if the engine starts to overheat. The CHT sensor transmits a signal to the

PCM, which moves the temperature gauge pointer into the red zone.

If the engine is not switched off and the temperature continues to rise, the Powertrain Check Lamp is illuminated.

This indicates to the driver that the engine is approaching critical limits and should be stopped. At this point DTC

P1285 is set in the PCM which can be retrieved using a scan tool.

Stage 2 of the strategy commences if the lamp and temperature gauge are ignored by the driver. The PCM will

start to control the engine by cutting out 3 cylinders and restricting load. The RPM will be limited below 3,000

RPM initially then will slowly be ramped down with time to as low as 800 RPM. Simultaneously the MIL

illuminates. This indicates that long term engine damage can occur and vehicle emissions will be affected. At this

point DTC P1299 is set in the PCM which can be retrieved using a scan tool." I checked PCM PIDs for both sensors and they appeared normal.
I had both both P1285 and P1299 DTCs set (read with Forscan). So... decided to change CHT sensor (easy, located by oil dip stick, inexpensive) and then CLEAR the DCTs because WSM says "

NOTE: The MIL can only be extinguished by using a scan tool after the fault has been rectified and the DTC

cleared." Cleared up all issues and have not had problem since (5K+ since). Good Luck

 

Would the sensor prevent any flow/pressure to the hoses?

 

Sensors should not effect flow or pressure. My thoughts were more directed at your situation in original "first paragraph".
Using a OBD2 reader or Forscan you should be able to determine what DCTs have been set, and also evaluate CHT and ECT temp
PIDs. Maybe original thermostat was not the problem. Note; CHT sensor is "one-time use" sensor, if removed or loosened it MUST
be replaced and the new CHT sensor torqued into place.