Ok guys I really need some help here. I am at my wits end. I have a 2004 Expedition 5.4L, 278,000 miles on truck. It has front and rear heat, I have no heat in either. Heat worked fine until I replaced the intake manifold due to a check engine light. (vacumn leak). I have flush both heater cores, flushed the cooling system, put a new thermostat in, and made sure the valve on the heater hose before the heater core was opening. I am going to take it to a repair shop next week if you guys don't have any other ideas. Thanks.

 

Have you checked the thermostat? As cheap as they are you may as well replace it with a new one.

 

Oops!!! I went back and added that in my original post. But yes I checked and replaced the original thermostat. The truck runs fine and the heat guage on the truck runs in the middle of the range. Thanks Sam.

 

Did you make sure you got all the air out of the system after flushing it? Air locks are pretty common.

Are the heater hoses both warm, both cold, or one of each (for each coolant loop).

This is not a complicated system. you have to have hot coolant circulating through each core then have air that flows through the air portion of the core(s) (heat exchanger). Break it down to the individual elements of what has to work and go through them in order of priority.

 

The inlet heater hoses get hot. The outlet hoses do not. Water is not flowing through the cores for some reason. When I flushed out the cooling system with the Prestone cooling kit I let the water run for at least 5 minutes. I did see some of the air come out then. I have no way a putting a vacumn on the system.

 

 

When I flush I disconnect both hoses to the heater core and run the hose straight to the core. After a bit I switch and run the water through the core in the opposite direction. You'd be surprised at how much gunk comes out sometimes.

 

I did flush the front core both ways. What gets me is it worked fine before I pulled the intake manifold. I has stopped working since I put it back together. Truck runs better than it has in a long time, just no heat.

Could the water pump possibly be weak and not providing enough flow to push through the heater core but enough to keep the engine cool?

 

Yex, it might be a bad water pump (eroded impeller), but the details you reported make me suspect it's a simple case of an air lock in the heater loop ... unless something got put back together wrong...

 

Any chance you put any of the hose back wrong?
If the water pump was an issue I'd think it would've been an issue before you took the manifold off.

 

Just wanted to update. I haved replaced the water pump and the radiator. (Radiator had a leak anyway.) No change. I took it to my local garage and had them evacuate the system, flush and fill. No change. The inlet to the heater core does get hot, the out let does not. One thing I didn't mention before. The return pipe for the heater core that goes under the intake manifold was leaking. I tried the youtube hack where I cut the pipe, installed an elbow and ran some heater hose around the outside of the block to the rear of the engine. The only thing I can think is that hose has gotten pinched under the intake stopping the return flow from the heater cores. Soooo I am going to order the correct part and fix it the right way. Damm the bad luck. I should have known better and fixed it the proper way to start with. Thanks guys.

 

Good luck and let us know if that fixes it.

 

I HAVE HEAT!!!! I went back and removed the youtube fix I had used. There just isn't enough room under the intake for the elbow and heater hose I used. The reason I used it is because I had read somewhere that the replacement pipe was around $150 bucks. Never checked. I know I am an idiot. Bought the replacement pipe from the dealer for around $30 bucks. Any way I want to thank you guys for all the replies.

Here is a good youtube video I used for guidance removing the intake manifold.
Here is the you tube video I used to bypass the heater return tube. My manifold doesn't have as much room in front as this one does.