Overheating...but not really

[nfancera]

Hey guys,

So I'm new around here but am coming in with a problem that has me completely stumped.

I have an 07 Sport Trac Limited V8 that has recently begun throwing warnings of overheating while running at highway speeds with either the AC or Cabin Vent on.

Once the temperature rises, if I shut off the AC or vent, it immediately drops back to normal. If I shut off and restart the truck the temp goes back to normal. If I continue however, I end up going into Limp Home mode.

Now I am fairly sure that the engine isn't really overheating as the temperature goes from pegged to normal within seconds of shutting off the AC or vent or restarting the engine. Additionally, there is no smoke, no boiling over, and I have no problems touching various components like the radiator cap.

I have replace the thermostat, the entire radiator and assembly and flushed my fluids, all with absolutely no effect.

If anyone has any ideas, I am seriously banging my head against the wall at this point. I would appreciate any advice.

 

[nfancera]

Just as an update, I've spent the night driving around with an OBD II scanner that can display real-time and have discovered the single, replicatable circumstance under which my truck overheats.

If my truck is running, regardless of speed, and the climate control is on and set below 70 degrees, my temperature gauges and sensors begin to climb immediately.

This happens regardless of whether the climate control is set to Auto, Vent only, Max AC, etc. If it is on and the temperature is set below 70, the temperature immediately begins to climb.

On the flip side, if the temp is set at 70 or above, the temperature will never climb.

Now that I know the circumstance in which the issue occurs, it's more livable, however it leaves me completely baffled as to the cause.