No heat most of the time.

Tiny
MATMO
  • MEMBER
  • 2004 FORD F-350
  • 162,000 MILES
My F350 is having a heat issue. Most of the time it blows luke cool air, but from time to time it will go from luke warm to barely warm. Just enough to defog the windows, but not enough to defrost them. I have already done quite a bit of work to try to repair it, replaced a couple of marginal parts, but so far no luck getting heat. Here is what I have done and the results after each repair.

1. The first thing that I noticed was that I was not always getting air to blow from the proper ports, the blend door was acting up. I change the switch in the dash and the blend door started working.

2. I was also smelling antifreeze in the cabin, this is usually a sign that the heater core is plugged. I replaced the heater core. Problem is when I checked the old core with water, there was no blockage that I could find.

3. I noticed that the heater control valve was not working properly. It was stuck half way open. Installed new heater control valve (might explain why the AC seemed a bit warm). I noticed that there wasn't any antifreeze in the hoses when I changed this out.

4. Started wondering if I had an air lock. I was able to hook up a Air Lift system to try to pull out the air lock. However I was only able to pull 10 pounds of vacuum. System says it should be 24-26 pounds. I could not find any visible signs of a hole that would prevent it pulling a proper vacuum.

My heating system is a closed loop system. The hose routing starts on the passenger side of the engine and then goes to the heater control valve, then into the heater core, then along the back of the fire wall to the drivers side where it tees into the hose coming from the bottom of the reservoir and then back into the side of the engine.

In the end I have two questions:

1. What could possibly cause the system to only pull 10 pounds of vacuum? No visible holes, no coolant leaks.

2. Could my water pump be going out? The engine does not overheat.

Of course any other thoughts are welcome.
Thanks, Tim
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Friday, October 11th, 2013 AT 6:36 PM

8 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
You have already done a lot of work. Is the blend air door working properly now? Also, have you checked for any vacuum leaks to the vent door system? You mentioned air wasn't coming out where it should. Is the engine warming up to a normal operating temp? Are both heater core hoses getting hot?

Let me know.
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Friday, October 11th, 2013 AT 6:55 PM
Tiny
MATMO
  • MEMBER
The blend door is working properly now. The switch on the dash that controls where you send the air fixed that issue. The air now comes out of the proper place when selected.

The engine temp is getting up to temp. BTW, this is the 6.0L Diesel.

The heater hoses do not get hot. This is one of the things that led me believe there was an air lock. I guess it is possible there could be a blockage in one of the hoses. They are 3/4" hoses so it would take something massive to plug them up.
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Friday, October 11th, 2013 AT 8:02 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
This will make a mess, but loosen the return hose from the heater core and see if there is circulation. There could be an air pocket in the core and doing this should release it. Plus, it will let you know if there is coolant circulating. Both hoses should be hot. If only one is getting hot, there is no circulation. Since the heater core is new, that leads me to believe there is an air pocket.
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Friday, October 11th, 2013 AT 8:06 PM
Tiny
MATMO
  • MEMBER
Ya, air pocket is still my best guess as well. Any ideas on why when I tried to remove the air pocket with the Air Lift System I could only pull down 10 pounds of vacuum? I would of thought that thing would of done the trick. BTW. Neither the return or supply hoses to the core are getting hot. It is almost like no coolant is pushing into the heater system at all.
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Friday, October 11th, 2013 AT 8:17 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Not sure why neither one is getting hot. Try what I said and let me know what happens. Like you said, it sounds like no coolant is flowing through the core.
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Saturday, October 12th, 2013 AT 10:33 PM
Tiny
MATMO
  • MEMBER
I was able to crack the lines and get coolant to flow out. Yes it made a mess. I have also tried to pull vacuum on the system twice with no real results. I took the truck out on the freeway and got her up to 85 mor 15-20 min. And checked the temps again. Here are the readings:

Engine temp - 185
Supply hose pre & pst heater control valve - 172
Return hose at exit of the core - 110
Return hose at the Y under the reservoir - 110
Return hose at the Y - 172

It seems that the air bubble is in the return line that runs from the core, along the firewall and back into the Y at the reservoir. As I said all attempts at burping it have failed. Any other ideas on how to achieve this?
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Sunday, October 13th, 2013 AT 5:33 AM
Tiny
MATMO
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I do want to try removing the return hose at the Y and then forcing water through the core and the return line to check for a blockage, and also to fill it if possible. I am having issues getting to the hose clamp that is in that spot at the moment.
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Sunday, October 13th, 2013 AT 5:37 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
I think that is what you need to do. As far as the temps, they seem normal.
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Sunday, October 13th, 2013 AT 10:21 AM

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