The heater core is constantly part of the coolant by-pass "loop" on '97 up XJs the moment the motor starts. On '96 down, coolant still flows thru the by-pass loop however, when the heater is "off", the heater control valve does not allow coolant to flow all the way to the heater core but rather diverts coolant flow (at the heater control valve) back to the water pump.

 

Since I bought my Jeep last year I have had no heat when idling. It was just luke warm. When running down the road it got nice and hot until I came to a stop then it was back to luke warm.

Well, this year now that it got cold out I had forgot to look into it until last weekend.

I checked the flow in the radiator and did a back flush of the heater core. I replaced the thermostat. Still no heat and temp was still above 210.

So, I got to looking on the net and seen alot of problems with the waterpumps like the photo on page 1.

I though that may be infact my problem. So, I went and bought a new water pump, bypass tube, and a new stat housing (old one was cracked at the lower ear).

I had called the dealer where I bought it and they informed me that they installed a new waterpump before I got the Jeep. It did "look" new but it could have been cleaned and reinstalled. It just felt like it was the problem to me and a few friends of mine.

I was going to tear into it in the morning but something just kept eating at me about the whole thing and I got out of bed and grab water jug and kept filling the radiator with water until it quit bleading air. I did this while squeezing the top radiator hose. I got about 1 gallon of water into the radiator. I could not beleive it took that much so far. Then I started up the Jeep and let it come to temp.....still no affect. Then I let the steam out of the cap and did it again. About another gallon of water! I started up the Jeep and BAM! Heat! and it runs right below 210.

It's been 3 cold days since and I have heat about 5 mins after start up. It will run you out in no time.

I then took back all parts and saved me about $70. The stat housing is not leaking and the bottom bolt head is holding the housing on nice and tight. I will relpace it later as I am short on funds right now.

This weekend I will drain out some of the water and replace with antifreeze.

Lesson learned, purge all air out of the cooling system unlike the dealer didn't do.

 

Greg,

I have little to no heat as well, I'm going to check into it like you did and report later...

wouldn't hurt to try...

thanks

 

Adding 2 gals of water to a cooling system that only holds 3 gals max?......and with the infamous 0331 cyl head?......yikes. Sure hope u start frequently raising the hood and inspect for leaks.

 

I recently replaced my upper and lower radiator hoses and thermostat and gasket on my 92, then replaced my heater control valve but I think I may have attached the hoses incorrectly... Or maybe didn't bleed air from the system adequately. I bought a Haynes manual but it isn't much help to a girl who may have taken on a bigger project than she could handle alone. Could someone please describe which hose goes where on the heater control valve since I'm obviously an amateur and didn't think to take a picture or mark them before taking out the old part? Lesson learned ...

 

as mentioned you might want to make sure you dont have cracking head issues as is common on your year

 

I ran into the same problem when I bought my 99. The owner said it overheated once. Well after everything was said and done the heater core was plugged and the radiator was plugged also. I took off both heater hoses from the motor and drained the coolant out of the hoses and made a flush with baking soda. I filled both lines up with the water and baking soda and wired them up so it would sit over night. Then the next morning I hooked up the flush kit I bought at o'reillys 4$ and back flushed the system. It took a while but know I have heat and both hoses are the same temp. Also check the radiator because the bottom of mine was clogged. The safe way is with a temp gun.

 

The heat in my 98 isn't all that now. But my AC clutch is crapping out on me now. Could that be related?

 

To the OP:

When I bought my 98 last November, it didn't have any heat either. The engine would warm up to normal spec, and not overheat, but the heater just blew cold. Thanksgiving weekend of last year I put a new longblock in it, along with a new water pump, t-stat, and radiator. Still no heat.

I finally took the heater core hoses off at the engine, and tried using my own lungs to blow through. Nothing. Next, took the air nozzle from my compressor, adjusted the outlet pressure down to 30 PSI, wrapped a bunch of electrical tape around the nozzle end, and wedged it in one of the hoses. Then I slowly released air into the hose. Pressure built for a couple of seconds and then all of a sudden, the other hose farted and a wad of crap came flying out that looked like the aftermath of a visit to Taco Bell on "all you can eat bean burritos" night.

After getting over the initial horror and uneasy fascination, I repeated this process several times. Then, I started pouring about two cups of water in one hose and blowing it through. Once I had it flowing consistently, if not generously, I went to find the CLR. I would put 1/4 cup of CLR in the hose followed by 2 cups of water, and then let it sit for about 5-6 minutes and then blow it out (all of the stuff was being caught in empty milk jugs). I repeated the CLR+water+5 minutes routine 3 times. Then I flushed the whole thing several times with plain water until it was coming out pretty clean. Probably ran a total of 4 gallons through there to flush all the CLR out.

I hooked it all back up and went for a drive. Within 5 minutes I had warm air coming through the vents. Within 10 minutes it was blowing hot. Within 15 minutes it would blow so hot at speed that I couldn't hold my hand to the center vents for more than about 30 seconds.

It's been a year and no problems so far. Perhaps I just got lucky with the CLR and my core walls were still nice and thick. But I have to think that if 5 minutes of CLR in the core is enough to eat through it, you've probably got a core that isn't going to last too much longer anyway, and you're probably better off finding out in your own garage than while moving down the road.

Just my two cents.

 

There must be a reason why the CLR web site says do not use CLR in a automotive application.

 

There is. It's liability. They don't have control over how people use their products, so they don't want people using it in things that could potentially cost lots of money. If you forget your shower head in a bowl of CLR and ruin it, you'd be out a $9 shower head. If you put 2 bottles of CLR in your Ferrarri's radiator and run it for 3 months, you'd be likely to sue the makers of CLR because you're clearly an idiot.
The product details don't always reflect what a product can do, just what the makers want you to do with it...

CLR is a great product for removing rust and calcium scale from cooling systems. So is hydrochloric acid, but you'd want to use that cautiously too.

 

I was being facetious. (guess I should have added or )

 

Yeah, sorry. I should've caught that. I just see posts all the time where people tell others not to put CLR in their cooling system or it will destroy it like it's written in the Bible. CLR is an acidic cleaner - Much less corrosive to aluminum and copper than the caustic crap that SuperFlush is made out of.

 

The back flush was probably doing the right thing, the core needs to be clear and to have low blockage. The output from your water pump will take the path of least resistance (always). So if the core flows but requires pressure to do so, you are sunk.

To test, fill one hose to the core with water, the other disconnected of course.
Raise the full one and make sure the water flows out with just the pressure of the raised hose.
Your garden hose has lots of pressure behind, much more than the water pump. So flow from the hose doesn't mean you'll get enough flow from your water pump thru the core.

Keep forward/reverse flushing the core until it flows freely and you've got heat. Use an additive if you like, will help unclog and clean the surface for better heat transfer (warmer air for the cabin).

Had a blocked core in Colorado which made my 45 min drive to Telluride in winter, before the sun rose, really interesting (jacket and snow boots).
I did the hose only backflush/forward flush for about 20 mins until it flowed smoothly and have had heat ever since (but I do periodically repeat to keep the core open).

Additives won't hurt and may help remove some surface contamination that will improve the heater somewhat.

 

Just a quick update, I've been flushing and back flushing my heater core ever 2-4 days and every time my heat seems to work better. I will keep doing this until I have a dragon for a heater! Every time I back flush it there is some crud that comes out. It's getting less and less everytime