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Unread 01-13-2012, 04:31 PM   #1
reeves_yj_88
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So heres the deal. I've encountered weak heat on various vehicles and it has always.boiled down to one of three things, coolant level, thermostat, or heater core. My 88 yj is a complete mystery. It has had weak heat since i got it. The coolant was low when i checked it so i topped it up. Still weak. Changed the thermostat, and the heat got hot again, but only for the first 10 minutes of my 40 minute commute at which point it starts blowing cold again. Both hoses at the heater core are hot to the touch when i check them after my drive. The lever under the dash on the passenger side that is controlled by the lever on the climate control panel on the dash is operating as it should be. I also have and 87 and a 95 yj, both of which throw heat like the surface of the sun, but my 88 is more like the dark side on the moon, just plain cold. It heats up at first then suddenly dissappears while driving after about 10-15 minutes. Up here im Canada i need my heat to work, especially as we approach february, when temps can get as low as -40 celcius. Can anyone help me out?

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Unread 01-13-2012, 05:48 PM   #2
Mean Max
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Try disconnecting the heater core hoses from the engine, then using only a garden hose, flush the heater core. I've seen many of them "cough up a hairball" and then work much better after that.

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Unread 01-13-2012, 05:58 PM   #3
Suprmn
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I agree with flushing the heater core. Along with that, the heater core fins could be plugged up. Also, after 24 years in Alaska fighting some of the same problems, this is what I would also look at. Is the hot/cold door fully closing? The cable or arm could be bent not alllowing the door to fully close. Does the engine temp hold or does it too fall while driving? If not, I would block off part of the radiator and see if that helps. If this jeep ever spent time in warm country it might have a bigger radiator. Happened to me when I bought one out of Arizona. Good luck, hope you find the problem. Being cold while driving sucks.
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Unread 01-13-2012, 06:34 PM   #4
reeves_yj_88
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Quote:
Originally Posted by Mean Max
Try disconnecting the heater core hoses from the engine, then using only a garden hose, flush the heater core. I've seen many of them "cough up a hairball" and then work much better after that.

Max
Thanks for the tips both of you. If the heater core was plugged tho wouldnt one of the hoses be much cooler than the other? The engine itself does maintain a steady temperature with the odd drop here and there. It runs a bit hotter since i changed the thermostat, wher the gauge reads 40 is where it used to sit, now it sits just below where the gauge reads 100. Maybe ill try blocking part of the rad, it does feel colder on the highway at 90km than thru the city at 50. If that doesnt help i guess the only thing left is flushing the core, problem of course is my garden hose is shut off and winterized for the season, lol.
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Unread 01-13-2012, 06:37 PM   #5
oldtime_ironman
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Flushing the core can *really* help as Mean Max pointed out. Ditto for the hot/cold blend dorrs, are they working right? However, what about the radiator cap? When mine got weak the temps were all over the place as it opened and closed. This also caused it to lose fluid.
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Unread 01-28-2012, 03:26 PM   #6
reeves_yj_88
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Well now I have replaced the thermostat and rad cap, tried blocking off 3/4 of my rad with cardboard and flushed the heater core twice. The second time I flushed it clear with water both ways, then filled it with vinegar (most popular alternative to corrosive clr), let it sit for 10 minutes then flushed it clean with water again for 10 minutes. I got my heat back for about 15 minutes, but even then it would only blow close to hot while accelerating, now its gone again. I also have an 87 parts yj which I ripped the core outta today. Gonna let it soak overnight, in a aluminum/brass/copper safe degreaser, flush it with hot water inside the house then flush it clean with cold water. The heat in the 87 works good anyway, so I figure if I clean it's core and swap the entire heater housing, hot/cold flaps and all, I should, in theory get my heat back. You have to remove the entire assembly to get to the core which is a huge pain as it is in an 87 with no ac. To have to swap it into my 88 with ac is going to be hell. I hate having to drop the ac to get at anything under my dash...

Anyway will let you know how that all goes.
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Unread 01-28-2012, 07:44 PM   #7
Old4X
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There is a vacuum actuator for the air door vacuum motor behind the dash.It's controlled by a switch on the heater control panel which is hooked up to engine vacuum.

Have you checked it?

Heat working at idle, but not under load sounds like vacuum related problem.
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Unread 01-29-2012, 06:09 PM   #8
reeves_yj_88
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Quote:
Originally Posted by Old4X
There is a vacuum actuator for the air door vacuum motor behind the dash.It's controlled by a switch on the heater control panel which is hooked up to engine vacuum.

Have you checked it?

Heat working at idle, but not under load sounds like vacuum related problem.
Didn't know there was one. I swapped the entire heater assembly, minus the intake duct and didn't see one, but there was one on the ac unit. Unless there is also one on the duct for incoming air, where is it located on the firewall? My heat is definitely working again after the swap, have yet to go the full commute though. Still not as uncomfortably hot as my wife's 95 yj heater, maybe this could have to do with the vacuum line you mentioned, the vacuum lines in this jeep are a mess from a p/o, some dangling, some missing, have yet to tackle that project, so if there is one that can affect heat, it probably is. If you can tell me where the actuator is located, please do. Thanks, Chris
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Unread 01-29-2012, 06:31 PM   #9
craniumboy
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i'd like to to see a pic of this vacuum line as well. i'm curious about crappy heat in my YJ and would like to check my vac lines to make sure they are right
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Unread 01-29-2012, 07:42 PM   #10
Old4X
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Here is an extensive discussion of the vac doors from several years ago:

http://www.jeepforum.com/forum/f12/m...es-why-499877/
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Unread 01-29-2012, 07:49 PM   #11
brentd711
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Wade through this thread for info on vent controls and vacuum lines.

eta....Old4X beat me to it
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Unread 01-29-2012, 08:00 PM   #12
95 Lowbuck
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Some times it's very hard to get all the air out of the system.
Some people park the Jeep nose up with the cap off and let it
run until it reaches temp, let it cool, top off the radiator, repeat.
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