Slick 99 XJ

Hello my Jeep Brothers!
;
SO i have a 1999 XJ, 4.0, 191*** miles, Stock, with the exception of a cone air filter set up.

I havent been getting good heat since I've gotten it and I'd really love to feel some warmth for once. Here are my symptoms:

*takes a while for it to warm up, and even then only hits up to about 180 or whatever 2 notches below 210 is.

*Air comes out barley WARM if at all when temp gauge it set to full heat and full blast.

I've checked coolant level and its good, swapped out thermostat to a new 195, flushed radiator, flushed heater core with compressed air with is controlled by a heater control valve that was installed by previous owner (looks like a garden hose lever) which seemed to flow properly when running water through it and both hoses on that seem to be same temp. I'm pretty much out of ideas on what to try next. it doesnt get crazy cold here in AZ but it'd be nice for those chilly nights. I appreciate all the help i've gotten from the forum in the past and know you guys can point me in the right direction. thanks!

EastBeast

I would verify that your temp gauge is working correctly but I would guess that the blend door isn't working correctly if you had a good flush of the heater core.

wahoo

Check and see if both heater hoses coming and going from the heater core are hot, if not your heater core is clogged. Check that all radiator hoses are hot also, if everything is hot then it has to be the blend door.

djb383

Make sure the heater hoses are very hot at the firewall (after the heater control valve). Verification of coolant temp with a infrared temp gun may help also.

Slick 99 XJ

Thanks for the input everyone. I'll double check everything again tomorrow after I drive it for a while. What should the normal operating temp be? Is the vent door a difficult fix?

d1mkaz

same problem here on 1998 2.5 td.

djb383

Two notches below 210 is 155F. If everything in the heater system works perfectly (good coolant flow thru the core and everything under the dash), 155F coolant temp will not make for a good heater....mediocre at best. If coolant temp is a verifiable 190-200, your gauge is screwed up, heater core is plugged and/or things under the dash are not working correctly.

Both heater hoses AT THE FIREWALL should be too hot to touch for more than a second or 2 if coolant is reaching proper temp AND circulating good thru the heater core. Several things to start checking......all components must work well together in order to have a good heater. Again, one of those infrared temp guns (+/-$25) is handy as a pocket on a shirt for diagnosing heater problems this time of year and overheat problems 7 mos from now.

Normal operating temp, especially now and for the next 5 mos depends mainly on what temp t-stat is installed. With low ambient temps, coolant temps will be right at the t-stat number, presuming everything in the cooling system is functioning correctly. My experience is a 160F t-stat makes for poor heater performance, a 180F t-stat works well and a 195F t-stat will roast wieners. One of those temp guns won't lie to you like the factory gauge is known to sometimes do.

The 4 key components for good heater performance are:

1. Hot enough coolant
2. Good coolant flow throughout the system
3. All heater core box flappers/doors working correctly
4. Good blower motor performance

Slick 99 XJ

Thanks DJB383 for that write up! I finally had some time today to look the whole cooling system over again, and after driving my XJ around for a good hour I popped the hood and felt all the hoses. I did notice that the heater core hoses AT THE FIRE WALL were just warm so i decided to drain everything again and give it another flush. After draining the coolant i gave the thermostat another look see just to make sure it was fine and not stuck open and noticed that it was actually a 160f one instead of a 195F like i thought (stupid me forgot to check before i installed the first time), so i went and got a 195F and after flushing it 2 times with a flushing kit and getting a 70/30 ratio of coolant and water it started warming up to 210 within a few minutes and I FINALLY started feeling some decent heat coming out!

Its not as hot as i'd like it to be so i'm guessing my vent door might be the problem now???? How would i go about fixing it???

Thanks for everyone's help so far, you guys are saving me lots of money and frustration!

Caish

Compressed air will not flush the heater core.
You need to use a garden hose and use water to BACKflush the core.
Start at the lower fitting so your running water in it and out the top.
This will flush any sediment out of the core, once it starts to look 90% clear reverse and flush from the top, till its clear or almost clear and then repeat the lower a second time too.
Then reconnect the heater hoses and give it a try.
As to a low temp with 195* thermostat I would want to verify there is not an air pocket in the head and that the system is not air locked so the coolant is just not getting to the core. Not sure on the newer 4.0's but on the renix there is a temp sensor on the head that can be removed and used to bleed the air from the head.

cruiser54

I just went through this today. Had a 195* Napa stat, which is a USA made Stant, and the heater wasn't hot. Replaced the stat with a factory model that has a floating BB in it with a corresponding hole that is to be mounted at the 12 o'clock position. Problem solved.

89Laredo

Follow Caish's suggestion... Ive also heard of putting CLR and water in it and letting it sit for 5-10 minutes, then flushing it again.
Also, Make sure you use distilled water only. Not tap water, when you fill the radiator or add water.

Slick 99 XJ

Caish,
I forgot to put that the first time I flushed the heater core i did use some CLR (looked it up on youtube) and it did get a bunch of sediment out. when I did it today I also did what you suggested and backflused it both ways before flushing the radiator itself, the water flowed through the heater core nice and steady and I kept doing it till it was mostly clear.I'm still checking fluid level after i've driven it. The flushing kit required that i cut the top heater core hose to install backflush valve thing witch i left open while filling it back up which was suppose to help eliminate air pockets, not sure how that worked tho.


cruiser54,
what do you mean by the 12 o clock position?













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cruiser54

The factory thermostat has a bleed hole with a BB in it on it's outer edge/flange that you install with the hole right at the top or 12 o'clock position.