My 2011 f150 3.5 eb. Is overheating when the outside temp is cold. Today went for a drive it was -25°F. It will over heat if I don't have the fan on high and the temp mix gage on the highest setting. I'm not losing any coolant and the charge is where it should be. This problem doesn't happen unless it's very cold out. I've also tried blocking off part of the radiator (gelling). But this made it worse.

 

Check the coolant to see if it protects down to -25F. It may be starting to freeze.

 

I did. The charge of the antifreeze is where it should be.