Can I get to the Heater Core without going through the engine. (Maybe the side wall?)

maybe thermostat or head gaskets gone.

Typically you will find the heater core sits inside the dash just inside the fire wall of the engine compartment, from the engine bay you can follow the water lines from the cooling system and water pump that go back to the fire wall and through to the heater core, find those to hoses together and the heater core is on the other side under the dash, usually under passenger side under dash behind the heater box, they are usually labor intensive to pull, and some require pulling the dash partly off etc.

Those hoses should be hot. You can grab them, but you won't hold on to them for to long. Less than a minute. Both heater core hoses should be hot. Radiator hoses will vary, but are still hot. If you can hold both hoses for the heater core at the fire wall without having to let go because of heat. Try to flush out the heater core(both ways through the hose) or replace it.

Your heater core is leaking. Replacement of this part is a big job and should be done by a professional.

Sounds like you may have water leaking out of your heater core.

This will cause an overheat condition, which you get because your engine cooling system can't pressure up as well.

You may also notice a kind of "sweet" smell to the air that comes from the air vents that blow when A/C or heater is on.

As water leaks into the A/C & Heater core compartment area...it trickles to the overflow drainhose on the firewall. This is usually intended for the condensation of the A/C core but a leaking heater core will drain that way too.

From what I hear, I'd see about disconnecting the heater core hoses going into the firewall and maybe use a splice to connect them to each other OR get a two 5/8 bolts and a couple clamps and plug the hoses.

This allows you to drive car without overheating and buys some time to get you another heater core (basically a "mini-radiator") Its summer, so you don't need the heater right now but keep in mind...you won't have a heater until the core gets replaced.

Hope this helps...

your firewall is between your engine compartment and the inside of your vehicle so if your out side with hood popped then the wall in the back is your fire wall hope this helps good luck

There are three thing that can go wrong here. I will give you the two simple ones first. first, check to make sure the thermostat isn't sticking or stuck. if it is, change it. two, Hot coolant going from the engine to the heater core, is controlled by a valve at the engine(these do go bad). Check the line when the engine is warmed up by turning on the heater(I know), and feel the line after about 5 minutes. The line should get hot, or very warm. The third is your heater core is clogged and needs to be replaced. hope this helps you

check youre heater hoses coming out of the engine .make sure they both are the same temp ,when the engine is warm going in to the heater core the hoses run up to the fire wall if the hoses are hot on both sides the problem is inside the car make sure the cable is moving form cold to hot if the cable is un hooked you will not have control over the temp .the cable runs under the glove box on the top of the heater box ,there is a small arm that moves back and forth ,the cable hooks up to a little clip make sure this is still attached if it is check youre controler on the dashboard the only way it would be a vaccume problem .is if the defrosters and heater and vents are not working .if this is the problem check for a disconnected vaccume line near the fire wall .or distrubitor

it makes no difference as long as you have coolant going it and out

http://www.chiltonlibrary.com/ContentViewer/CVFrameset.aspx
Here is a link for you if you want to replace the heater core your self with common tools. As for the heater hose, you should see two small radiator hose going to the fire wall. You can disconnect the hose from the fire wall and connect them together, this will by pass the heater core till you replace the bad core. Good luck and keep me posted, be glad to know your expedition is running 100% again.