Hi all...new to this site but enjoying all the info already.
Hoping for some help with 2007 F250 6.0L, with electronic temp control

Truck has intermittent no heat in the cab
Thermostat replaced
Coolant temp good
vacuum ok as all vents work
coolant level full

problem started only at idle now happening while driving

outside temp is -30F, any help is appriciated

 

I have a hand vacuum pump that I use for bleeding the brakes and testing vacuum-powered components on the vehicle. I bought it at Al's, before it became Schuck's, before it became O'Riely's... anyway, it wasn't expensive and it has a guage. You can try to operate the heater water flow valve with a hand pump and see how much vacuum it takes to trip it. You can then hook up the pump to your vacuum line with the engine running and read how much vacuum you have. I did this to my truck and fixed the heater, the brake-boost, the 4X4-shift-on-the-fly, and I think the turbo... but I'm still learning my truck.

 

When the engine is completely warmed up and you are driving on the highway, does the heater ALWAYS work, or is it intermittent then too?

 

barebones
when hot and on the highway it is always hot

Tugly
i removed the shutoff valve from the system to eliminate that as well

 

Could the new thermostat be in backwards?

I.e., maybe you had a problem with the old thermostat going bad, but with the new thermostat the problem went from intermittent to constant?

At least we know the heater isn't plugged....

 

thermostat only goes in one way. one piece unit, thermostat with housing.

i am leaning towards heater core plugging up as i had the dash apart today and all blend doors and air ducting works fine.

used compressed air and blew threw the core... heat is back for right now.

i will flush the cooling system once to warms up a bit.

will keep everyone posted

 

Sounds like air pockets in the coolant passages. Have you run it up hard to redline at all? Sometime high rpms help push out the air, other times it takes steep inclines to help it out.