Truck heater not getting as warm as normal

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Stacy Waldrep

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Apr 24, 2009
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Location
Lake Park, MN
I need some help. I have a 2004 Trac 4x4 that isn't producing heat as warm as it normally has in the past. The engine temp gauge reads normal. When I turn the temperature knob to cold, it blows cold air and when I turn it to hot, it blows barely warm air. I replaced the thermostat last night just to make sure that wasn't it. It didn't help at all. I can see that the vacuum controlled heater control valve on the heater hose moves when I turn the heat off and back on so I assume it's working right. Any ideas on what to check next? Could the blend door be working partially? I need good heat...please help.
 
Checkand see if all the heat is coming from the defrost vents. If so check the vacuum tubing connection behind the glove box. It might have comme off. Our there may not be any vacuum on it. That is what moves the blend door.

Also the heater valve under the hood might be stuck. Not circulating enough hot water.

The level in the radiator maybe low. The t-stat, might be stuck wide open. The temp gauges' in our tracs are really useless as far as the true temp goes.



This is just some Ideas' of what to look at.
 
Ok, I'll answer your suggestions first, Eddie. The air blows wherever I tell it to with the normal force. It's just not warm enough no matter where it's blowing. I already looked at the heater control valve under the hood and it seems to move and work fine. The coolant level is fine and I just replaced the thermostat hoping that would fix the problem which it didn't make any difference. Any other ideas?



Zudnick, I just did a flush of the system a few months ago so I wouldn't think that would be a problem. I'm sure I could be wrong though.



Thanks for the responses and keep suggestions coming so I can figure out what this is.
 
I agree with Zudnick that clogged heater core might be your problem. See ericthecarguy dot com for a good video on this. He has good tips on checking heater hoses before/after heater control valve and heater core. I'd definitely do this before considering heater core replacement. Let us know what you find.
 
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Yardsale, the last time I remember it working right would be probably February or March, the last time I would have really needed heat. I don't remember if it was getting really hot at the start of this winter cause I haven't really needed it until the last month or so.



Vic, I just reverse flushed the system back during the summer. I don't see the heater core getting clogged up since then. My coolant and radiator look totally clean. I'm sure I could be wrong and I'll make sure to look at the website you posted and test some more things.



Thanks for the responses.
 
The system was flushed a few months ago, but the last time you remember it working well was six months ago (February or March). Was the heater tested after the flush? Seems if it were, and it worked, the last time you remember it working well would be then. If it wasn't tested, then maybe the flush didn't work.



The heater core is relatively small with small channels; a small blockage is a large percentage of the potential flow.



I (only) assume that it has been long enough that there is no air trapped in the system.



That's all I have for now.
 
Yardsale, I flushed and changed my coolant as just routine maintenance back during the summer not because something was wrong. With nothing being wrong, I didn't think to check and see if heat worked or not after the flush. I just know for a fact that my heat worked fine last winter and I don't recall if it got really hot this past September, October, or early November as it wasn't really cold then where it would have been noticeable as it is now.



When the engine is at normal operating temperature, the upper radiator hose and the two heater hoses are warm to the touch but not really hot. That's one reason I changed my thermostat cause I thought they should be warmer to the touch than that. The thermostat change didn't seem to make much difference with that though.



I'm not sure where to go from here. It's too freaking cold outside to do much work on it and I don't have enough heat in the truck to be comfortable. It sucks.
 
The flush probably broke loose a bunch of crap and it clogged the heat core. I would pull the hoses off the core and flush them both directions with a garden hose. If you clear out a bunch of crud, I would also reflush the entire system and refill with fresh coolant and distilled water.
 
I probably should try that Gavin but it's below zero outside right now so using a water hose is out of the question. I could probably try doing it with an air hose while in the garage. If there was a bunch of crap in the heater core, wouldn't I see some of that in my radiator? When I drained the coolant partially to change my thermostat, there wasn't the first sign of any crud or anything. The radiator also looked perfectly clean when looking down in there.
 
Stacy, if the heater core's plugged up, the debris ain't gonna make it to the radiator. Jes' sayin'. With engine and heater on, try a temperature feel on the hoses into and out of the heater control valve. If you've got hot water downstream of valve, then valve is working. Now try same for hoses in and out of heater core; if return line isn't at least warm I'd say you've got a blocked heater core. Good DIY video for this on ericthecarguy.
 
Vic, maybe you're right about debris not making it to the radiator but I find it hard to believe that if there's so much stuff in the system that the heater core is plugged that there wouldn't be any debris anywhere else. Maybe you're right though. I did already post stuff about the temps of the hoses. The upper radiator hose as well as both heater hoses get warm but not as hot as I think they should be. There isn't much difference in temp between the two heater hoses. The inlet hose may be slightly warmer but it's hard to tell. I looked at the ericthecarguy site and he said he thinks a clogged heater core is pretty low on the list of things to check if your heat isn't working. I've gone through a number of things on the list though so I may be getting down there. Both hoses are warm, not hot but warm, so I don't think it's plugged. I may try blowing it out anyway though unless someone can point me somewhere else.



I wonder if the temperature blend door or the actuator can be partially working. I don't hear any clicking or other noise when I change the temp dial. It will go from cold to slightly warm and back when I turn the dial from cold to hot without any noise.



I appreciate all the responses.
 
Stacy, I found this HVAC diagram on site sponsor Fast Parts Network. Maybe it'll be of some help. Do you have a Haynes or other shop manual? I feel for you living up North with weak heat. Gotta have it! Good luck and let us know your progress.
 
Thanks, Vic. Any information is helpful at this point. I do have several shop manuals. I'm going to keep trying things until I hopefully figure it out. I'll make sure to post updates and if anybody has any more suggestions please post them.
 
If your heater hoses are not hot, that would further confirm a blockage of the heater core. If the core was not blocked, the inlet hose would be as hot as the upper radiator hose. If a blend door was not working, the outlet hose would be hot as well.



I think you found the problem. Blocked heater valve or clogged heater core.
 
Gavin, you may have misunderstood my description of the temp of my hoses. The upper radiator hose and the two heater hoses are about the same temp, warm but not hot. Even the upper radiator hose doesn't get hot like burn your hand hot. That's why I thought the thermostat may be sticking open or something so I changed it. So, my heater hoses are the same temp as the upper radiator hose, warm but not hot.
 
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Hi Stacy,



My symptoms (2004 XLT -- well maintained) were the exact same as yours... Coolant looked fine -- good colour, good level -- just no heat. I changed out the thermostat too thinking that might be the problem. That didn't do anything.



Flushed out the heater core and it fixed everything. Give it a try when you get a chance.





Z
 
Zudnick, yeah, I'm probably heading that direction. It's just such a pain to do when it's so cold. I can't do it with water because of the cold so I can only use air like in the ericthecarguy videos. I'm still a little confused as to why my upper radiator hose doesn't get really hot to the touch. I put in the stock temp thermostat but before and after the thermostat change, the hose only gets warm. I'm used to having that upper hose get pretty hot.
 
I replaced my T-stat and housing.... Had same issue for years..... Bad t stat.... Problem fixed.



Todd Z
 

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