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Unread 11-12-2011, 01:54 PM   #1
zachjf
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1998 ZJ 
 
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5.9 heating woes...

I know this is like beating a dead horse and I would have posted this in one of the existing threads but my issue is different than most so bear with me....

Ever since I bought my 5.9 I've had a heater issue which has so far eluded me. I've read all the threads, done all the tests and compared my results against other vehicles with properly functioning heaters and yet I still can't track this thing down. I know for a fact the following are installed and functioning properly;

1) Blend door - works fine and cycles back and forth from low A/C temp to the high setting, also verified by pulling climate control codes.
2) Heater core - not plugged as both hoses get equally hot, can't hold onto them for too long.
3) Blower - pushes huge amounts of air and works as it should.
4) Thermostat - Opens and closes fine, tested with a cold engine that sat overnight *but* this is where I'm starting to wonder....

It took literally 15-20min of idling to get the thermostat to pop open which seems like kind of a long time for a 5.9 with 0 airflow through the engine bay, granted its only 48 degrees out right now but I would think it shouldn't take that long to warm up even idling. During summer (70deg + days) it warmed up quick and always stayed right at 210 but now that the temps have dropped (mid 40's during the day/mid 30's at nite) I am lucky if it warms up before I drive 10miles. After I let the engine sit idling and the thermostat popped this is where my temp gauge sat, and usually sits while driving;



The temp coming out of the vents is lukewarm at best, nowhere near what the climate control panel is set to and not even close to what the heater in my TJ put out or what my mom and brothers XJ's put out. I could literally drive around in my used up soft top TJ with the window open in a t shirt when it was 30 degrees out and still be toasty warm but this damn ZJ I have to keep the windows up and wear a jacket just to make it tolerable. I'm starting to think my thermostat is the culprit as the other 3 Jeeps I have to test against all run right at 210 and have great heaters.

Anyone else had an issue like mine where the normal issues don't apply?

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Unread 11-12-2011, 02:08 PM   #2
KoreaZJ
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You may have a 180 thermostat. I have a 180 thermostat in my 4.0L, my temps run about the same as your gauge pic. With the stock thermostat, it was closer to 210. During a cold start, the temp gauge starts to move with a couple of minutes and the heater air starts warming. My heater may run a bit cooler with the 180 thermostat , but still warms the cabin well, even when temps are in the single digits. Does your heater housing feel hot under the dash? Mine cooks after everything is warmed up, can barely keep a hand on it.
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Unread 11-12-2011, 02:31 PM   #3
zachjf
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I'm thinking about just throwing a new thermo in it and see what happens. I can't think of any other reason why the air is not warming up to a decent temp besides the coolant not getting hot enough to keep up with the airflow over the heater core. I did notice that when I sit with the engine running the temp does increase till I start moving then it drops off. My gauge moves after about 2-3min of starting it but its really slow and I get cold air out of the vents till the point where I took the pic, at that point the temp out of the vents is probably low to mid 70's.
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Unread 12-02-2011, 04:49 AM   #4
zachjf
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Finally got around to putting a new thermostat in today. The one I removed was a 195 and I replaced it with a brand new 195 and there's no change. Temperature on the gauge is exactly the same as before and I still only get lukewarm air out of the vents. The FSM says the heater air temp fully warmed up, which in my case is only showing 175'ish on the gauge, from the floor vent in ambient temps of 50 degrees should be no less than 141degrees and after testing mine its at roughly 115-120.

I'm seriously at a loss as to where to go next because everything seems to work exactly like it should except it just wont heat up. The best I could get the interior warmed up to while idling in park was 74 degrees and dropped down to 66 almost immediately after I started driving.
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Unread 12-02-2011, 05:28 AM   #5
KoreaZJ
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ATC receives feedback from the cabin temp sensor under the dash, could be fouled or bad.

Have you done the self-diagnostic tests?
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Unread 12-02-2011, 05:45 AM   #6
zachjf
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yep, I get 00 from the atc self diagnostic. After changing the thermostat I know the issue is cooling system related and not anything with the hvac itself. If I can figure out the reason why the engine is "underheating" I'm sure the heater will fix itself. I am at a loss at this point, dealt with plenty of overheating vehicles before, never an underheating one
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Unread 12-02-2011, 06:01 AM   #7
KoreaZJ
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I don't have a 5.9, but my 4.0 throws warm air before the temp gauge needle reaches the first mark above 100, and it only takes 2-3 minutes idling.

What if the ATC is not controlling the blend door properly? Then it wouldn't matter how hot the heater core is, you still might get lukewarm/cool air. Can you confirm the blend door position? Or disconnect the actuator and swing it manually to the full hot position?
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Unread 12-02-2011, 01:40 PM   #8
zachjf
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I dont get any hot air at all, its lukewarm at most and thats only when the gauge gets to the point shown in the picture which is maxed in all but super long idling, 20+ min. The main issue is the fact the engine isn't getting fully warmed up. I think I'm going to replace the water pump, radiator cap, double acid flush with CLR and if that fails I'm gonna put a 210 thermostat in it for winter cause I'm starting to get annoyed!

I had to get up at 7am to give a friend a ride to work and it was 30 degrees out and I froze my *** off the entire time i was driving, 45min round trip!
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Unread 12-02-2011, 01:58 PM   #9
KoreaZJ
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If you reach under the dash is the heater core hot? If it is, you should get warm air.
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Unread 12-02-2011, 02:13 PM   #10
Snap-on
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did you purge the coolant system yet?
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Unread 12-02-2011, 02:27 PM   #11
zachjf
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Snap-On;
I changed the thermostat and burped the system according to the FSM; replace thermo/refill/run till hot/refill overflow bottle/repeat till overflow level stays constant. I changed the thermo a few days ago and coolant level is constant between hot/cold checks.

KoreaZJ;
Nope, box doesn't get hot like it should or put out the FSM rated temp but neither do the rad hoses or heater hoses. Issue is definitely somewhere in the motor itself because I can open the radiator cap when it shows the 175'ish on the gauge. i think I might pull the new thermo and toss it into a pan of water on the stove and check its opening temp. I'm also gonna drill a tiny hole, 1/16th or 32nd, into the thermo to help with the air bleed, not sure why the new thermo doesnt have a bleed on it
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Unread 12-02-2011, 02:38 PM   #12
Jeepfordan
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What brand thermostat did you go with? Ive had a few that we're bad out of the box
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Unread 12-02-2011, 03:12 PM   #13
Snap-on
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silly question but does your radiator cap hold pressure? have you done a pressure test on the coolant system
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Unread 12-02-2011, 03:42 PM   #14
zachjf
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JeepFordan;

Its a Stant thermostat. i've always used them with good results but its starting to look like I maybe got a bad one. I still have the old one so I'm gonna use the pan of water on the stove trick with a thermometer and see exactly what temp it pops then do the same to the new one and go from there.

SnapOn;
Its a newer Stant cap, PO had it replaced with the pre-sale checkup so its less than a year old. I dont have the cap/system pressure tester but I think I can take mine into Autozone and have them check it.
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Unread 12-02-2011, 05:49 PM   #15
Candymancan
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Quote:
Originally Posted by KoreaZJ View Post
You may have a 180 thermostat. I have a 180 thermostat in my 4.0L, my temps run about the same as your gauge pic. With the stock thermostat, it was closer to 210. During a cold start, the temp gauge starts to move with a couple of minutes and the heater air starts warming. My heater may run a bit cooler with the 180 thermostat , but still warms the cabin well, even when temps are in the single digits. Does your heater housing feel hot under the dash? Mine cooks after everything is warmed up, can barely keep a hand on it.


He doesnt have a 180 degree thermostat, all 5.9's in the Jeeps sit at that temp on the gauge. Its the electric fan thats keeping it so cool, the dodge 5.9's with the clutch fans are usually warmer sitting at 210f. The Jeep 5.9's are always at 200f.

If you do the math on that guage where his needle is sitting at right now its at 195-200f.

As for heating issues, my 5.9 only takes 1 mile to heat up to 200f. If i let it sit it takes awhile, but when i drive it it takes exactly 1 mile. But i too still have issues with my heater..

If i set it to say 70f after the engine has warmed up, the heat will be really toasty. However after awhile it will start to get really cool. So i have to keep raising the temp constantly in order to keep the heat going. The other day i had to eventually turn it up to 80f in order to keep toasty. However even then the air would seem to get cool again but then randomly get warm again. I dont know why its doing this, but its freakin anoying. Other times the air is soo hot it burns my fingers on the steering wheel and thats when its only set to like 72f, i have to turn it down to like 67 or so.

Un like the original poster i have had my coolant changed about 2-3 times this year due to me replacing the water pump and timing cover gasket, and stuff. Before i did all that i had the system flushed and filled with new coolant, then when i replaced the old cap is when it started leaking everywhere so then i had it drained and replaced the pump ect.
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