Have flushed the coolant system and the heater core lines. Still no heat. I am wondering if my water pump is not strong enough. My 2001 f150 xlt 5.4L has 265000+ miles yet it does not overheat. I noticed that the upper radiator hose has no fluid in it when engine is cold. There is no sign of water seeping out of the weep hole. I have never lost any coolant but noticed that when I flushed the radiator yesterday it reminded me of the dark red soil of western Oklahoma. I changed the thermostat and the o-ring also.

 

the water pumps ford use last a long long time that said yours sure has but I would replace the thermostate first use the stock 195 one. The blades in the water pump have been known to corrode off when they get old so you could be due for one be make sure you have a nice new correct stat first.

 

Thanks for the reply. I have changed the thermostat and o-ring. I am going to pull the water pump and see about its condition.

 

Ok, look at this thread and post 19.Here are pictures of my waterpump and of my new one.I had the same thing for coolant as you.Also I did run into some other problems, like a rusted out intake tube for the heater core, and a leaking lower intake gasket.

https://www.f150online.com/forums/v8...al-tool-2.html

 

You probably have a clogged heater core.

 

x2. i had a pin-hole sized leak in my radiator and added some copper stuff to clog it and it also clogged my heater core. very thin lines

 

It may just be the reducer in the heater core hose also may have some crap blocking the flow.I would take a old t-stat and cut the guts out of it, and install it and then start truck to see if you have coolant flow.