Jason Mullins

97 f150 5.4 have been having heater issues. Ive changed thermostat, flushed heater core, and radiator checked blend doors, and everything works as it should. Truck just doesnt put out much heat. Ive burped the system several times so i know theres no air in it either. When u first start the truck it goes give a small amount of white smoke but it doesnt stink any. No signs of coolant on oil dipstick and i never have to add antifreeze to it? System just acts like theres a problem somewhere not allowing it to build up any pressure! When the truck is at operating temp the upper radiator hose doesnt hardly carry any pressure at all? Im new to fords and im running out of things to look at or check any help is appreciated!!!!!!!! Thanks

Carcrazygts2

Have you changed the hoses? Degas chamber cap? There are alot of things that could cause it. Even a broken blend door motor.

Jason Mullins

The puke tank cap could cause lack of pressure???

Carcrazygts2

Yes. If its not sealed it will never create pressure.

Jason Mullins

Ill pick one up tonight and see if that helps any. Could it also cause the lack of heat not getting very hot?

Carcrazygts2

No. Even if the system was open the truck would still get to operating temperature. Are you sure that the T-stat has not failed?

Jason Mullins

I just changed the tstat 2 weeks ago

Carcrazygts2

It still could have failed and failed open. What brand did you buy?

Jason Mullins

Its a duralast from autozone

Carcrazygts2

Take it back. Get a Stant or OE motorcraft. I have seen them fail open and closed before. They are cheap for a reason.