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Heating problems! ITS COLD!

2233 Views 33 Replies 8 Participants Last post by  6ohPowersmoke
Ok guys so here are my issues. I probabaly should have looked into this before the cold weather but it hadn’t bothered me until temps have been in the 20-30 range.

problem #1 my heat is not working kind of. It was working intermittently the past few months but has gotten worse (or so it seems) while working intermittently it would range from blowing cold to luke warm to hot and all in between with no rhyme or reason. I have checked me degas bottle and the coolant level seemed to be a little lower than normal but not drastically lower than my line. (I checked it after a cold soak) it seems like it wouldn’t blow any type of warm air until the truck was up to temps then would intermittently blow warm. It also seems to blow warmer if I have it set on 80 compared to 90. Could the slightly low coolant level be the cause? Am I correct with what the coolant level should be after a cold soak? My degas bottle has a molded line and I have a sharpie line below that

problem #2 my driver seat heater does not work. Passenger works great and gets hot. Drivers seat has the red light on the button come on but no heat. I have read it could be a bad relay, I do not hear a relay click On when I hit the driver button. Wheee is the relay? How do I change it?

also to note, I have not noticed any coolant leaks so the drop in coolant level, although minor, has me puzzled.

it is deleted and studded with a coolant filter on there
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Also just to note, my A/C during the summer was also kind of spotty. It would blow but not also very cold and would take a while to blow cold. Not sure if it’s related or not.
Do you mean the hoses leading into the heater core?
Yea, I’ve just went down a lot of rabbit holes with this reading a lot about heater core, radiator, hoses, coolant, valves etc and it’s all gotten jumbled in my head so I just wanted to make sure. I’ll check those on start up in the morning
Ok I started the truck. Waited maybe 3 minutes and felt the hoses. Both were warm but not hot yet by the time I got to work both were much warmer. The vacuum valve stayed in the same position no matter what setting it was on. It was facing the cab of the truck (running parallel with the hose) The heater air did not feel warm after waiting a few minutes but I did not check it when I stopped.

where is the plug for the heater fan? Also my truck doesn’t have the dial style controls it’s the style in the picture below. Does the blend door still work the sane way With this style?

degas cap is as old as the truck I’m guessing so I will replace that for good measure as well


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No leaks around the vacuum. It springs back, but it does go back to the starting position. With koeo I tried to listen for the blend door while cycling through different modes (a/c-heat-off) and did not hear anything.

I guess I’ll start there
Replaced the actuator and can’t tell much of a difference. The vacuum valve isn’t moving when I switch from heat to a/c to off. Should it? Also I’ve seen where some trucks have a small vacuum hose on top of that valve. Mine is on the back. Is that correct? Am I missing one?


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does the air flow speed/power seem to be the same in all settings? feet, vs body, ve defrost or does it seem to blow harder on defrost than all other settings?
I haven’t noticed there being a difference but I’ll be on the look out for that tomorrow
Hose in in the correct place -- but as stated before you do not use that valve in the winter -- only OFF and Max AC

Most likely you have other problems in the vacuum system -- we need to address your current problem first
pick up a hand held vacuum pump that has a gauge from someplace like harbor freight or amazon -- for testing , later
I will have a better idea if the actuator worked or not in the morning 1plus drive at 5am in 28 degree weather should give me a good idea. If that’s not the culprit what would be next?
Ok here’s the update. It was definitely warmer this morning. I had it on max temp and max fan. I wouldn’t consider it hot but it was warm. I guess that better than nothing. Any reason it wouldn’t be getting as hot as it should?

I was hoping there was a relay on both seats and maybe that was the problem with the drivers. I don’t have anyone ride with me much. Are the seat elements interchangeable? Might just switch them
Also it only felt the warmest after the truck was up to temp and I was going down the highway at 75. Once I got off the interstate and slowed down it cooled down and was blowing more luke warm air
Now that sounds like a slipping water pump. Still have an OEM plastic pump?
As far as I know yes it’s oem
I was thinking vacuum pump problem. Didn't see a post mention that.
High speed- high enough vacuum to work stuff. Slow down and the heat actuator and blend door may not have enough vacuum.
Is that the pump that’s behind the passenger battery? Could that also cause some a/c problems? Because during the summer I had some a/c do the same stuff. It would get cool but not cold
My bad, I wasn't paying attention to the model year of your truck. You do indeed have an electric pump. That wouldn't be affected by engine speed. At least I don't think so. None the less, it may be worth a look at to make sure the pump cycles. If there is a leak somewhere it could deplete the vacuum needed to operate stuff.
Do your auto hubs lock when you put it in 4x mode? They are vacuum operated. If they don't lock it could definitely be vacuum related. I'm not really up on the 6.0 so don't want to send you down a rabbit hole without a hooka smoking cat in it.
Mine has manual locking hubs
Title of the thread says it all here "Heating problems! ITS COLD!"
I think you also have Cooling problems ITS HOT

Just a different season -- same old problem

We talked about the blend door -- but little feed back on if it works or not
We have not talked about air flow or if the core is plugged up with junk -- internally or externally

I think until you are willing to do the work -- just gonna have to put up with the HOT and COLD situation
and yeah, vacuum pump plays the role in where the air comes out of the HVAC system, so there is that one also
Felt like I did give feed back on the actuator. Installed a new one, which I said in a earlier post, it has not made much of a difference that I can tell. Maybe lightly warmer but not hot. I have noticed that it is significantly warmer when at highway speeds or when I am heavy on the throttle. If my ect is 194-196 air is warm. If it’s 190-192 (at idle or just cruising around town) it’s cold.
Had to make the trip to town this morning for some new skins on the old International Dump Truck
Fired the 6.0 up and went in the house to get the Grand Kid ready
Heard the 6.0 idle up, He already had his shoes and coat on, we grabbed a drink of water and out the door
Was 20F at startup, so got the Boy in the truck and popped the hood to feel the heater hoses
Front supply beside the alternator was nice and warn, maybe 120 ish
Return under the degas bottle was a little warm -- the heater was on Auto and was blowing hard at that time
Radiator and upper hose was cold
Heater was putting out warm heat already -- not it will get hotter -- but remember this as only at about 10 minutes form start @20F

Turning the temp down to cold, made cold blow from the heater -- Back to 70F made warm in only a couple of seconds
Luckily it isn’t that cold where I’m at. Only 30f this morning. Still cold enough to annoy me. It’s take several minutes of driving and engine temp has to be up significantly before any type of somewhat warm air blows. Before truck is up to temp or if I stop and idle it blows cold

if the actuator wasn’t the issue would heater core be the next place to look? Or possibly water pump not circulating enough coolant, which would explain spotty heat and a/c?

or could itbe something as simple as burping the system? I had to open last summer for a Tstat change and again in September and early January for a coolant filter change could air bubbles gotten in then causing this?
Ok I’ve been doing some research and watching some diesel tech ron YouTube. Could the heater vacuum valve be the culprit? Is there a possibility that that has failed partially open? As in if it’s half way open/closed on the inside of that valve it would restrict the flow of hot when the heater is on and would allow to much hot when the a/c is on, which would cause both to not work as well as they should?

don’t think I did a good job of explaining that but hopefully someone understands what’s I’m trying to say
The hose on the RH side where it connects to the water pump is the supply
Then runs back to a vacuum valve before entering the heater core
Look for heat there first

The vacuum valve should be in the extended position -- it is only closed when the controls are OFF and Max AC
Soon as you feel heat in the supply line, it should also be in the return -- wait till the heat feels pretty warm to the touch -- then go feel the heater air

You can pop the plug off the heater fan, and key on -- if it is quiet there, you should hear the blend door motor as you operate the temperature -- should move smoothly with no clicking
Check this again this morning. The hose with the valve on it was warm. The other was cold. Check it after about 10 minutes idling and after a few minutes of driving as well.

It was 26 this morning. Truck warmed up to temps fine. 192 driving around. But when parked it would drop down to 186 and stay steady there. Deltas are 5-7.

Potential causes
Plugged heater core?
Failing valve?
Failing tstat?
Failing vacuum pump?
Air in system?

in the picture the hose with the valve was warm. The hose just behind the ziptie Was cold


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