I am at the end of my rope here. I don't know what to do next. I have a 2003 Expedition with the 5.4. I only get heat every once in a while. Lately not at all. I've changed the Heater core(it had a leak), the blend door actuator, thermostat, and the climate control unit. The thermostat came apart when I lifted it out so I thought that was the problem, but no luck there. What else could be the problem?

 

Btw, I'm leaning towards a blown head gasket. I'm getting pressure in the coolant system even before the engine is cold. Also, when I open the coolant fill cap, the air that comes out has that combustion smell. I'm thinking the air pockets getting in the system aren't letting the coolant cycle. That's why sometimes it gets through and a get a minute of heat. Any theories?

 

Mike have you done a leak down test on the closed system yet? Your symptoms strongly suggest a head gasket unless there are other oddities about our Modular motors unknown to me.

You might try posting this in the Cooling, Heating, Ventilation & A/C forum too----might be someone there whose been through this same scenario.

 

Just went through this with a 4.6l, see my post.
Sounds like you have hg leak, and maybe pump problem too.

Check your water pump flow. You can disconnect the upper hose at the radiator, keep the system full with a hose in the radiator, and let it warm up. Once warm (opened thermostat) the water pump should flow like a fire hose when you rev it up. It should throw water clear over the front of the truck. Mine was rusted away, but it still pushed water out the hose, and it fooled me.


To confirm whether you _also_ have a head gasket leak, try this.

Start with cold engine. Fill the system completely full of water. Park on an uphill if you can, you want it to have zero air left. Close it up, run it for 3 or 4 minutes, NOT long enough to warm it up. If your hoses are pressure tight, and if you get a big splash of cold coolant when you open the cap, you have a head gasket leak, maybe from a warped head. That is about $700 in parts and head fixing, and 11-15 hours labor at a good shop. Mine is costing $1400 M&L.