Heat blowing warm not hot..

I picked up a cheap 90 XJ Sport, 4.0, manual, only basic options except for AC. It sat for a little over a year before I picked it up. Anyway I'm having troulbe with the heat. It will only blow warm. I do not have a temp gauge, only a light that comes on when it's over heating (one of the dumbest things about this jeep) so I had no idea if it was even warming up, so naturally the first thing I did was replaced the Thermostat. That helped slightly, it went from cold air to luke warm air.

Well this past weekend I started losing a ton of coolant, it ended up my reservoir was cracked. I replaced the reservoir and went back on my quest for heat.

So from there I noticed the hose going into the heater coil was hot but the hose coming out was luke warm. I did a reverse flush on the heater coil, now the bottom hose is hot like the top hose. This helped some more, I went from luke warm air to warm air, but not hot. I read up on the coolant system for my jeep and apparently it is a pressurized system. So I burped the system at the temp sensor. Still only warm air.

My brother (who has an XJ) then told me about how he had to replace the heater valve in his, he said you can tell if it needs replacing by holding in the button on the heater valve and the air will get hot. We tried this on mine but the air actually got colder instead of hotter.

So I'm kind of at a loss, I could greatly use some recommendations on things to try.

BTW, yes the temp slider works on the dash, so it is not stuck in the warm position, but it does not completely go to cold, maybe 3/4 of the way through cold, it feels like it's hitting something. I don't think this affects the heat though, but that is just a guess.

First thing, lay under the dash and see if the heater control cable is moving the door all the way. You could even disconnect the cable at the end and see if the door moves further and increases the heat. Did you use a 195 degree tstat? You can also eliminate the heater control valve under the hood. Later models don't have them and many people just eliminate them.

Sounds like you had multiple problems and you have most of them solved.

If both top and bottom hoses are getting hot then you have solved the first problem of getting hot coolant to the system.

The next step is making sure the blend door under the dash is working properly. It sounds like it is not swinging freely and is getting hung up on something in side the ductwork. Follow the cable from the temperature control slider (the thingy that you grab to make the temp hotter of colder) or where it enters the duct work under the dash that is where the blend door will be.

Sometimes you can grab the cable and force the door to work, and sometimes you won't get that lucky and you will have to take the thing apart and clear out the obstruction. Not to worry it's not that hard to take apart.

:repair:

Yes it was a 195 degree thermostat.

I will check the door and see if I can come up with anything.. cross your fingers.. I need heat

Replace the heater control valve (or eliminate it)....they're cheap.

You mentioned that you backflushed the heater core and that it improved a bit. You still may have enough blockage inside the core to give you lukewarm air. Be forewarned that if you do get to this point, replacing the heater core is a very labor intensive job. Part is cheap but if you have a shop do it, you'll get killed with labor. Get a procedure and do it yourself.

Get a hold of a point and shoot infrared thermometer and point it directly at the thermostat housing. Looking for around 200 degrees give or take a bit.

I'm curious as to the condition of the vacuum lines and vacuum reservoir.

When you lose all vacuum to the HVAC the default position is defrost only.

You could have insufficient vacuum to properly move the blend doors, but enough vacuum to keep the system from going to default.

Check the vacuum reservoir, passenger's side of the front bumper. The vacuum line running to it likes to break around the battery. Good move is to relocate the vacuum reservoir into the engine bay, I put mine under the cooling system pressure bottle. Gets rid of about 7' of vacuum line.

Do you have a NP231 or NP242 transfer case? If you have an NP231--2wd/4hi/4lo part time transfer case then you have a D30 vacuum disconnect axle in the front. Major source of vacuum problems.

I would check the vacuum system over closely.

It must be the 231 as my 4wd did not work at first due to the vacuum line coming off of the axle, once I put it back in place it worked fine.

I did not get a chance to look at the door yesterday as it rained all day long. Hopefully I'll be able to look at it today.

If I do end up replacing the heater coil I will do it myself, I've done these in the past. The only work I wont do myself is body work as I majorly suck at it.

Buy, rent, borrow a simple vacuum gauge.

"T" it in to the vacuum line, run the engine for a couple of minutes and then shut it off and see how long the system holds vacuum. That will tell you if there are leaks.

Chasing your tail.. Blend door on a 90 is not vacuum controlled but the mode doors are.

However it is critical to make sure the cable is moving the blend door all the way. The heater core could be hotter than the hubs of Hades but it won't blow hot if the blend door is routing intake air around the heater core.

try taking the heater hoses off at the heater core, cover the distributor and coil and run a decent pressure hose through it until all the gunk stops coming out. i don't know but its worked good for me on two xj's so far

Eric96Xj said:

try taking the heater hoses off at the heater core, cover the distributor and coil and run a decent pressure hose through it until all the gunk stops coming out. i don't know but its worked good for me on two xj's so far

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Does any one have pics of the heater core?
I dont even know where to look/what the little bugger looks like...

/noob

Open the hood. passenger's side firewall, two heater hoses with hose clamps right at the firewall--in and out for the heater core.

You are better off the loosen the clamps and then split the hose in a couple places to gently remove it. If you try twisting and pulling you will likely end up having to replace the heater core because you broke it.

joe_peters said:

Open the hood. passenger's side firewall, two heater hoses with hose clamps right at the firewall--in and out for the heater core.

You are better off the loosen the clamps and then split the hose in a couple places to gently remove it. If you try twisting and pulling you will likely end up having to replace the heater core because you broke it.

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I ended up disconnecting them on the other side of the hose up by the thermostat. It worked pretty well and gave me more room to work.

I had to use a pressure washer because no gunk came out when I used the garden house. Not even really any water, just a little dribble. The pressure washer sure cleaned it out tho. Some one warned me about cracking my heater core with it, but so far so good.

Final result: I have LOTS more heat. 500% improvement. Still isnt as good as some other heaters, but it really made a difference. I would recomend doing this before anything else involving your heatercore. Cheap and effective.:05of5:

CherBear said:

I ended up disconnecting them on the other side of the hose up by the thermostat. It worked pretty well and gave me more room to work.

I had to use a pressure washer because no gunk came out when I used the garden house. Not even really any water, just a little dribble. The pressure washer sure cleaned it out tho. Some one warned me about cracking my heater core with it, but so far so good.

Final result: I have LOTS more heat. 500% improvement. Still isnt as good as some other heaters, but it really made a difference. I would recomend doing this before anything else involving your heatercore. Cheap and effective.:05of5:

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I don't know what kind of weather you are having, it is going to be 22-23 degrees here tonight, but weather permitting--when it isn't going to freeze, you should get a good commercial rad flush, not the 15 min junk, the kind you put in and drive for 500 miles. Prestone is good. Follow the product directions and it will dissolve a lot of buildup in the entire system.

Is there also a vacuum controlled heater valve near the hoses to the core? They have a habit of sticking partially or all the way closed.You can move the lever on the side by hand to see if it's stuck somewhere in the middle of it's travel.

joe_peters said:

I don't know what kind of weather you are having, it is going to be 22-23 degrees here tonight, but weather permitting--when it isn't going to freeze, you should get a good commercial rad flush, not the 15 min junk, the kind you put in and drive for 500 miles. Prestone is good. Follow the product directions and it will dissolve a lot of buildup in the entire system.

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Yes I run prestone ussually. I hooked the top hose back up and started the Jeep back up, letting all the water flow out into a bucket. Then I filled the radiator back up with prestone. I might need to burp the system, im sure there is a few air bubbles after this little escapade.

Just an update.. I still do not have much heat, just enough to take the edge off of the cold.

On a side note. Can someone take a pic of the heater hose routes for a 90? I'm starting to think maybe the previous owner hooked something up wrong as the return hose from the coil is hotter than the inlet hose. Actually the whole system is like like that.

Also if we press the button on the heater valve the air goes from cold to warm, does this mean it is working correctly since it will get hot when it does not?

If you have the interior control on hot, but can monkey around with the heater valve under the hood to make it hotter, that means that the valve is NOT working properly. Eliminate the valve for best results.

winterbeater said:

If you have the interior control on hot, but can monkey around with the heater valve under the hood to make it hotter, that means that the valve is NOT working properly. Eliminate the valve for best results.

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No the heater valve causes the heat to blow cold (well what little heat I originally had).