I have read numerous threads and most do not show what the fix is. OP never posted if issue was fixed. So here is my issue and I will post the fix.


First, things I've done. Replaced the motorcraft 185 degree tstat with a 192 stant. I did this about 200 miles ago. I removed rear panel to take out the blend door motor and found it in working condition. It rotated when I adjusted the manual temp dial. Rear inlet hose to rear core is VERY hot to the touch (ouch). Front inlet hose to front core is much hotter than outlet hose as is the rear.

Issues: front heat is Luke warm, say 90 to 100 degrees after a 30 min drive.
Rear heat is Odd...sometimes it's Luke warm like front and sometimes like this AM it was actually cold. And yes all three temp dials are on hot just so I don't screw that up.

I did actually take off rear panel a couple months ago because I did not think ac was cold enough. But after taking panel off and turning ac on it was cold again.

I am 3rd owner and it looks like the radiator was replaced within the last few years, it just looks newer than other parts.


Questions:

How do you flush rear core?
Any good write ups on rear core removal?

I am leaning towards plugged cores and a intermittent blend door issue.
Unless someone has a better guess?

EDIT: checked heater hoses for rear core after drive to work and now both are COLD!!! How can this be?

 

Excursion?

Check this heater bypass valve. It's supposed to stop hot coolant from circulating to the cores to provide better A/C in hot weather.



Excuse all the other stuff in the pic, was doing Uppipes at the time

This is often done as a Mod on the trucks, but the Excursions include it OEM.

I believe it is vacuum driven, so check the small hose you can see on it.

 

Yes it's a 2000 excursion.

I will buy a cheap autozone valve and see if that helps. If it does I will order a OEM unit for when the autozone junk fails.

Thanks, I will update with results tonight.

 

Went to lunch and rear air was Luke warm instead of cold.

Switched to max AC and rear air went cold, even with heat dial on max red hot setting. Switched back to heat (no AC) and rear air is very very cold. Checked inlet and outlet rear core hoses and both are really hot. One is a little hotter than the other.

I bought a heater control valve, and will install it.

I still think part of my issue is a weak or intermittent blend door aculator. Hope the Luke warm issue is the valve.

 

Hot heater hoses in the rear, yet cold air? Does sound like the blend door back there, but doesn't explain your upfront cool?

Sure about your thermostat? Not upside down? The Stant I bought leaked. The OEM didn't

I just replaced my rear blend door motor this month: https://www.ford-trucks.com/forums/1...l#post15686911

Be sure to set your rear heat all the way COLD first, as the blend door is spring loaded and will be on cold without a motor

I was told that part AFTER I did the work, but luckily it is where it was when I did it.

If your valve above is messed up, it might be working intermittently, partially, not at all, etc.

Do you have ESOF 4wd? Do they work? Any other vacuum leaks you know of that could be stopping it from working?

 

I do have ESOF. It works good, after I went thru lock outs.

I would think that my selection of vent, floor, defrost would be affected if I had a vacuum issue though, right?

I will hook up my obd2 scan tool and Varify ECT when I get home tonight.

 

It defaults to defrost when vacuum is lost.

I don't have ECT on my Excursion. EOT, but only the trucks had ECT.

If the hoses are warm in the rear, you should have heat. If BOTH hoses are warm in the rear, coolant is flowing through the rear coils. Doesn't mean they don't have junk in them or the lines, but not completely clogged.

I am going to go out on a limb and say to try indexing that rear blend door motor first, replace it second.

The diverter valve up front is your call. You could probably put a pipe coupler and a couple of hose clamps in there from Home Depot to test (it would eliminate it.

Then you would know to go to order a valve, or to keep looking at thermostat and blend door motor (About $30 online, or from a junkyard, same as top vent/floor motor)

Hope this helps. My daughter was really happy when it started getting cold this month and I fixed the rear heat for her

 

I am just going to through parts at it until it's fixed.

1st was thermostat, I wanted a 192 to 195 anyhow.
2nd will be the heater valve.
3rd will be the blend door motors.
4th will be heater cores.

Basically easiest to most difficult.

Nice to know the temp **** should be in cold setting prior to installing a new blend motor.. thanks

 

Yeah, nothing really expensive there

1. My opinion, replacing the thermostat with OEM (Ford Dealer) gives the Tstat with gasket anyways

2. Do you have the top radiator hose that goes through or around the serpentine belt? If through, you can get the one that goes around ("2nd alternator coolant hose" I think it's called). You don't have to remove hose later to change your belt

3. The intermittent nature of your problem could be the door or the valve. The valve can be removed from the equation for about $5 in parts to test it and you'll know the next time your truck coolant is warm enough to put out heat. (Turn off front heat, it is faster to test. Ask me how I know)

4. Heater cores can always be flushed. Did you convert over to ELC? Last time you flushed your system?


Outside of a control failure or waterpump failure, of which I don't see any reason to suspect either of those

You have a plan that *should* fix it. Bypassing the valve after replacing the TStat (look for gunk in it or other signs of failure) seems to be the quickest and easiest.

I had a time replacing the rear blend door motor. Not hard, just a lot of "stuff" to get to it, including unloading all the "stuff" I carry in the back!

 

The ECT (engine coolant temp) was 197 degrees when I got home.

 

Ok, had time to put a new blend door motor on rear system.

This fixed the cold air issue on rear.

Please note you should set temp controls to cold prior to dis-assembly. I also had to plug in new blend door motor and start motor. This moved the actulator gears enough that they lined up with the door that was in the down position.

Still only have warm air in rear, front is warmer than rear but no where near as hot as my other excursion.

Next is the heater valve.

 

That's awesome!

Now you're into the realm where flushing your rear heater core may help.

My rear doesn't get as hot when the front heat is on. Take it for a drive, warm it up good, running rear heat and front system completely off.

But progress is always a good sign

 

Drove to work today. Front and rear heat is only luke warm.

Lines to both cores are very hot.
Lines from both cores are hot too but not quite as hot as inlets.

I think it's a heater core issue. Maybe PO used some stop leak or something. As I think radiator is newish.

I'm going to R&R heater cores.
Found good info and video on removal of front core, but cannot find one scrap on rear core.

Hope those quick disconnects are not too difficult to remove.
Guess I will just dig into it this weekend.

 

So, I bought 2 new heater cores from NAPA. Both have new insulation on them.

I am dreading trying to get my big hands back up under to fire wall to try to disconnect the "quick" connectors for front core.

I have not had anything apart yet, so I need to ask this question.

Is there a way to cut the core tubes from inside, and just snake them out from engine bay? This way I can easily remove the quick connectors.

 

Sorry, can't help you there

Did you replace that thermostat? I am using the OEM 195*F The old one was pretty cruddy.

Might be a good time to flush the whole system and switch to ELC, if you are so inclined