My 2000 Excursion with a 6.8 and 210,000 miles was always an Alabama truck until June of this year when I ran away with it to northern New York, near the Canadian border. On cold days — anything below 15º or so, the rear heater blows nice and hot but the front heater blows barely warm air at best — it's more like mildly cool air. I don't like it; my wife won't tolerate it. And I like my wife!

For fun, I changed the thermostat — replacing the existing 180º one with a 195º one. Of course, no change (in either heater core).

Four questions for I am wrestling with:

First, my research influences me to consider reverse flushing my front heater core... even though I had the entire cooling system flushed a few months ago. Thoughts?

Second, in the picture, what is my finger pointing to? (If it is relevant, my truck does not have automatic climate control — it's bare bones.)

Third, I realize that the problem may be associated with the blend door. Which is easier, tinkering with the blend door or reverse flushing?

Fourth, can someone please! post a picture of the hoses I would detach in order to flush the front heater core,

Thanks! And, merry Christmas.

 

Before doing anything else, check the relative temps of the heater inlet and outlet hoses when the system is fully warmed up. You have to determine if there is hot coolant flowing through the core in order to figure out what has to be done. Anything else is out of order.

You are pointing at the vacuum-controlled heater valve. It's supposed to get vacuum when the HVAC control is set to MAX AC and should close, cutting off the flow of hot coolant through the core. With no vacuum applied, the valve should be open and coolant should flow through the valve freely. The hose from the valve should go to one of the heater core's ports and there should be another hose that connects to the adjacent port.

If hot coolant is properly flowing, both hoses will be hot, painfully so if you aren't careful.

 

Very, very simple and clearly written reply. Very helpful. Thank you.

A question about what you wrote: The question is —and I have not gone out to look yet, I assume the hose from the valve that goes goes down is the one that goes to the front heater core (and the one that goes horizontally and to the rear goes to the rear heater core)?

 

Go take a look. The heater core ports stick through holes in the firewall, it will be obvious when you look at it.

The SUV has additional plumbing for the rear that is not present on my P/U so I can't look at what you have.

 

When you turn your key on without hitting the starter, can you hear the vacuum pump running?

Climate vent select and that heater valve are all vacuum controller. You might have a bad pump or a leak?

Can you make the mid vents blow? On our 4WD, when there is a vacuum leak, the vents default to defrost.

 

The OP, ITSOT, would have to turn his key all the way to START to hear his 10 cylinder vacuum pump run.

 

So I was fighting a cold heater up front earlier in November. I too replaced the thermostat.

I was messing around under the hood cleaning up a mess the Prior owner had made. I found that my vacuum canister (big football black plastic thing) on pass fender wasn't correctly hooked up. All of the vacuum lines were wrong.

Using the vacuum diagram on the radiator, I pulled everything loose and correctly connected it all. While I was at it, I messed with the vacuum valve (your finger was pointing at). With the engine running I would connect and disconnect the hose to it. Not positive, but I think I "shocked it" into working.

My heat now blows wonderfully hot on the 15F day like today. My powersteering pump ain't happy, but at least I'm warm

 

Vacuum is irrelevant to the basic task supplying of heat to the cabin. Absence of vacuum would cause full coolant flow through the control valve and all airflow would be directed to the defroster as these are the default operations with no vacuum.

The 6.8L IS the vacuum pump, there is no other vacuum pump (this is not a diesel).

 

I don't understand. You mean there are OTHER FUELS out there? LOL.

Thanks for the reminder.

 

Wow. Y'all have been busy here. Thanks so much to each of you. I think I'm... smarter now. The jury is still out on this.

So, last night was minus 20º and the high so far today is 0º, which makes it a great day to tinker under the hood. Not. But I did anyway. Mostly because I have to take the family in it for 7.5 hours tomorrow.

What I found is, the feed to the front core is very hot — I can touch it only a few seconds. But the return from the core is only warm — I could hold it all day if I wanted. (But it is warm!) What now?

(Again, the rear heat is blowing very hot.)

Thanks again.

 

The vacuum seems to be working well: My ESOF works (I fixed it myself this summer), and all the different vents work, etc. Thanks!

 

Fascinating. And thanks for replying. But, as the hose past the vacuum valve is hot, hot, hot, the valve is working. Or, if it is not working, it is stuck open, which is good enough until summer!

By the way, I revitalized my ESOF by doing the same thing, essentially. I kept pulsing the diaphragm in the hub with an air compressor... and now it works.

 

Just to be clear: I have full coolant flow to the heater core. And all vents are selectable and operational — defrost, floor, and everything in between.

Thanks.

 

Flush the core.

 

Just tidying up some loose ends...

I reverse-flushed the front heater core and all works well!