So I just bought this nice 99 ford expedition with a 4.6l
My problem is I have warmish heat when I keep my fan on low.
But as soon as I crank it up it. Cools down. I've been doing alot of searching
And can't find a definitive answer. It acts the same front and rear.
And the hoses don't seem to get so hot I can't hold them!
So here's what I have done already

Changed Tstat
Changed water pump
Flushed water through the heater core seemed fine

It seem like both heater core hoses get hot
Not super hot though! And the upper radiator hose stays fairly limp
Like its not building pressure. So I have searched all over
And I see similar problems . But i don't know what to look at next.
It seemed like it warmed up sitting at a idle . And my temp
Seems perfect.

So when I got home from work I looked it over.




Well here's where I'm at now.

I cut a hole in the heater box from the glove box
The heater core get nice and hot
Both sides. And the blend door works flawlessly .
So here's what I noticed while looking over everything.
The upper hose was limp until the truck
Fully warmed up and then it had a little pressure in it
. And it doesn't get burning hot like it should.
And I felt the lower hose and I was cool not warm at all??
The coolant is full and the trucks temp
Is perfect. So what gives ? Please I'm begging for help!

 

If the radiator hose are not getting hot, then the problem is with the t-stat...new or not.

1. What temperature t-stat did you install?
2. Did you install the t-stat so that the spring faces the engine?

 

I bought the Tstat at advance auto.
I beleive its just a stock replacement.

And yes it was installed correctly.

I guess I will grab one from a ford dealer today and give a
Try tonight.

 

Same thing going on with my 2004 Expedition, see thread below.

 

Similar but different.
My truck heat up to operating temp and stay there.
And I get a little heat.

 

My front heat was lukewarm before getting cold (rear was always lukewarm) until I backflushed the heater cores, a simple flush didn't remove enough sediment to make a difference. I flushed repeatedly backward and forwards until it ran clear. Made a world of difference it gets nice and hot now.

 

Good info !

I think I'm going to drop it off for a coolant flush.
Do people have good luck with these?

 

Same problem for me too, 2000 eddie bauer with the 5.4 Engine, temp gauge reads in the middle but warm, not hot heat. Changed the T-stat with new, 190 degree and did nothing. Stinks driving around with weak heat. Thanks god I have other vehicles.

As for coolant flushing, if the vehicle had antifreeze in it it's whole life I dont see how sediment could have accumulated and caused such a problem. I need to check my hoses and radiator with my handheld temp gauge.

 

Well I just flushed the whole system
Out . And it didn't look bad. The only
Other thing is if the fan is stuck on cooling
The truck too much. I have no clue what else it could be.

 

That's good. But did you specifically disconnect the heater cores and flush them in both directions?

And did you remove the block drain when you flushed the "whole" system?

The thermostat will keep the engine from becoming too cool.

 

I'm on my second new thermostat.

 

Got it. But the point I was trying to make is that even if the cooling fan is stuck on, the thermostat (if its working correctly) will not let the fan cool the engine too much.

Did you specifically disconnect the heater cores and flush them in both directions? Multiple times?

And did you remove the block drain when you flushed the "whole" system?

 

Yes I flushed them separately . Forward backwards. Flushed everything
Out.

 

So, if your confident that the coolant is flowing through the heater core, and the heater fan is pushing air through the heater core, and the blend door is in the full heat position, can you look in the hole you cut in the heater box and determine if the heater core fins cools off after running the fan on high?

We're trying. Do you have the EATC system?

 

I will try to see if the heater core cools down
Tonight when I get home from work. It did seem better
This morning on the ride to work.

No it has the basic heating system with the dials.