All,

I have a 2013 F150 with the 5.0 and my ford sync and 85k miles. The thermostat seems to be good as the fan blows high when I first start the truck anticipating the truck to warm up.

Problem is that when I drive around town (downtown traffic) the heater only blows cold / cool air, not heat (when I have the heat turned up to above 70 degrees,.. mainly set around 77-85 range. And the heat does not work while stuck in traffic ( which I have bee in for up to 30-45 mins), however, when I hit the freeway and rev up RPM's the fan blows heat (to the temp. I have set on the thermostat).

I'm thinking it might be a pressure differential sensor or valve.... but I have no idea!

HALP!! Any ideas?

FYI I had the water pump replaced 5 months ago....

 

Low on Coolant maybe.

 

X2 on low coolant. I just discovered a leaky water pump on my 13 3.7. It was the same way as yours until the revs were up.

Last weekend it got a new pump and coolant, nice and toasty now.