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No/low heater air, searched but need guidance

gba88

NAXJA Forum User
Location
PA
Hi Guys,
This is on a 99 that I helped my friend buy. The PO had a flush/fill valve put in on the top hose that goes into the heater core, and the reserve tank was well below the "add" line. I filled the tank.

After reading all kinds of info I have bought a new 195 thermostat (not installed yet), and am thinking about flushing the core. Supposedly the core was replaced just in 07 (the guy had receipts).

I'm concerned b/c after a trip yesterday, both in (top) and out (bottom) hoses to the core were really hot, but yet, no hot air from the vents (warm at BEST). So, does this definitely sound like the core needs to be flushed, or could it be just the thermostat? I'm just looking for as much info as I can find before getting into it.

On a side note, the PO told me that he had shop put the flush/fill valve on because "all jeeps have a problem with the cooling systems gunking up". I have never heard/read this before, was he possibly referring to the pre 91 closed systems? Also, should I do away with the "T" cap/valve assembly and replace it with a stock hose? Thanks for any help!
 
Well, after more searching in a different direction, I found info that it may be the blend door. From the info I posted though, is there *anything* else it could be? Also, I'd still like to hear opinions on the flush valve that the PO installed (If it should be removed or not). I'm concerned about it because I saw a web page somewhere where a guy had installed one, then the cap cracked spraying the entire compartment with coolant...
 
Check and make sure that the vacuum lines are still in place.
 
Sorry forgot to say it's a 99.......... I have a BAD feeling that it's the blend door. Could the in and out hoses to the core still be hot and the core need to be flushed?

EDIT: dang, guess i DID mention it's a 99....so just all the vac lines under the hood? I thought the blend door via the motor controlled all the hot or cold airflow? All vents blow air and change to defrost/vent/floor...and the ac blows cold too. When you switch the temp to highest heat though with ac knob changed to vent only, only warm air comes out. It's prob only warm too b/c it's like 70 degrees out.
 
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Update: I observed the motor that moves the blend door, and the motor and the door both seem to be working.

I put the AC on, it blew cold, then I turned it to hot, and it became luke warm...so I'm pretty sure that the door MUST be working to some extent in order to block off the cold AC. At first I tried it without the AC running, but it was too hard to tell a temp change (plus I only let it idle for about 3 minutes or so, so prob not even heated enough to feel significant heat). I just figured that if I turned on the AC and it was able to block that air, that the door must be working.

So I guess I'm back to the thermostat or a clogged/crapped up core...I didn't check any vac lines, since I'm not sure which to check and how they'd play a part in the system. Any help would be appreciated, Thanks
 
OK. You've given us a lot of information here, but we need to organize it systematically. Good news, AC is cold. Good news, both heater hoses are hot. Do you have a temperature gage? How hot is the engine running? Engine should be running about 210 degrees to get good heat. If not, it indicates a thermostat issue. If the heater core was blocked, both hoses should not be hot. It seems like either thermostat or blend door. I wouldn't remove the flush valve as long as it is not leaking.
 
OK. You've given us a lot of information here, but we need to organize it systematically. Good news, AC is cold. Good news, both heater hoses are hot. Do you have a temperature gage? How hot is the engine running? Engine should be running about 210 degrees to get good heat. If not, it indicates a thermostat issue. If the heater core was blocked, both hoses should not be hot. It seems like either thermostat or blend door. I wouldn't remove the flush valve as long as it is not leaking.

Temp is right under 210 (right around where my 96 and 99 run), so it seems ok. I already bought a thermostat and gasket, but I'll have to wait til the weekend to try that. If it were the blend door, wouldn't cold air still blow through when I turn the temp the whole way up with the AC running? I can clearly see the plastic gear part running it's course as I adjust the temp, and there's definitely a detectable change in the airflow as the temp knob is turned.

edit: thanks for the post btw and the info about the flush valve! It's not leaking as far as I can see.
 
I'm interested in this as well because the 98 that I bought last month seems to do the same thing.
 
Could be that your system is low and gotten a bubble in it. My XJ would stop blowing hot air when the coolant got low. Happened to me offroad last winter. My motor was tired and used coolant, when it got low enough I would start getting cold air through the vents. Add some coolant and I was good to go.

If your blend doors are working I would think that the vaccum isn't leaking. The default of no or low vaccum to the heater controls is that it blows to only defrost vents.

Wish I could help more and I hope that I'm understanding the issue correctly.


Parakeet
 
Could be that your system is low and gotten a bubble in it. My XJ would stop blowing hot air when the coolant got low. Happened to me offroad last winter. My motor was tired and used coolant, when it got low enough I would start getting cold air through the vents. Add some coolant and I was good to go.

If your blend doors are working I would think that the vaccum isn't leaking. The default of no or low vaccum to the heater controls is that it blows to only defrost vents.

Wish I could help more and I hope that I'm understanding the issue correctly.


Parakeet

Thanks! Well, the PO didn't mind the overflow tank much, and it was almost empty when we got it. I filled it up right away though, and it has remained at the full level. I'm going to do the thermostat this weekend and go from there I guess. I'm really convinced that the door is working, because it was definitely blowing cold then warm last night during a test run.
 
ive no idea how it happens or even IF it happens, but i would say to check you havent got an air pocket trapped in your cooling system. I cant see how this happens but i believe air can get trapped possibly in the heater hoses or the heater core itself? It wont do any harm to burp. My heater hoses are fire hot after a run and impossible to squeeze shut with a naked hand. They also feel full. When i had luke warm heat last year, i claimed my heater hoses were hot, in reality i could clamp them tight for 5 or 6 seconds before i got burnt. Your fix may well be elsewhere but id back up what parakeet said as a next port of call.
 
ive no idea how it happens or even IF it happens, but i would say to check you havent got an air pocket trapped in your cooling system. I cant see how this happens but i believe air can get trapped possibly in the heater hoses or the heater core itself? It wont do any harm to burp. My heater hoses are fire hot after a run and impossible to squeeze shut with a naked hand. They also feel full. When i had luke warm heat last year, i claimed my heater hoses were hot, in reality i could clamp them tight for 5 or 6 seconds before i got burnt. Your fix may well be elsewhere but id back up what parakeet said as a next port of call.

Thanks! How exactly do I go about doing this?? Prob. a dumb question, but I've never done it before.
 
yeah thats a half XXXX way of doing it but its the way that i done it. You can find a much better way of doing it but this way worked for me.
Remember though to remove the radiator cap from a cold engine.
The coolant on an xj should rise up and start to spill out and over the top of the radiator. This is normal on the xj. Youll wanna catch that coolant, but then the level should start to drop, the trick here is to keep it topped up and make sure that no more air gets sucked back into the radiator. As long as you keep it topped up near the top of the neck you should be ok. You should not see any bubbles coming up at any time. Rising level yes, large bubbles no.
Id keep at it a while. Also after youve done that if you have a friend, get him to rev the engine, as he does this, the level will drop a fair bit. With good timing you can pour an extra bit of coolant in to keep it topped up. Then with the engine still revving replace the radiator cap securley. This will allow you to get extra coolant in there. Any excess will just go into the overflow. Once its cooled down id replace the radiator cap.
 
If burping baby doesn't help, I'd look back at the blend door closer. It's just a couple of screws to pop the actutor off the door. Then you can actually move the door back and forth by hand to see what it feels like and how the air changes temp. This should convince you finally about the door function.
 
Thanks a lot, guys! Looks like this weekend I'll be getting into all this. I'll prob just flush/burp the system and install the new thermostat at the same time. If none of that works of course it will be back to the blend door (maybe it could be "half" working and just making it warm instead of hot). Thanks again :)
 
If you decide to flush your system the way in which you have posted in that link and your system is full of crud. I promise you, you will be doing that till the cows come home. You need to flush through the entire system including the block and back flush the entire system. Theres many posts on it. To give you an idea, when i was in the navy, we were taught that one tea spoon full of oil, will contanimate a 10 metre square surface of the ocean. The cooling system appears to be similar in that a tea spoon full of crud left in any part of your cooling system will contanimate ALL the fresh water you put in.
 
If you decide to flush your system the way in which you have posted in that link and your system is full of crud. I promise you, you will be doing that till the cows come home. You need to flush through the entire system including the block and back flush the entire system. Theres many posts on it. To give you an idea, when i was in the navy, we were taught that one tea spoon full of oil, will contanimate a 10 metre square surface of the ocean. The cooling system appears to be similar in that a tea spoon full of crud left in any part of your cooling system will contanimate ALL the fresh water you put in.

Thanks for the head's up. The guy we bought it off of actually made a big deal about how he had the flush valve put on and how clean he kept the coolant. I actually searched and found a bunch more posts on here (naxja) with what would prob be the hardcore ways to do it. I'm not so worried about flushing it as I am just making sure there's no air in the system.
 
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