poor heat from heater core - JeepForum.com

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post #1 of 6 Old 09-07-2008, 07:56 PM Thread Starter
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1998 TJ Wrangler 
Join Date: Apr 2008
Location: Michigan
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poor heat from heater core

I have 2 problems here that i cannot figure out. 1st problem is my heater core. Even when my 98 TJ is warmed up i get warm not hot air if im lucky. I have had the heater core flushed once and that seemed to fix the problem for about a day. What do you guys recommend? Flush it again? replace heater core? 2nd problem has to do with my air vents. If the AC or heat is on any speed other than low...when i accelerate, sometimes the air will switch and only escape through the defrost vent by the windshield on top of the dash. All advice is greatly appreciated.

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post #2 of 6 Old 09-07-2008, 08:01 PM
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1998 TJ Wrangler 
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Location: Greenfield,IN
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I have a 98 TJ and a 98 YJ. I had the same problems with both. Reverse flush heater core. disconnect both hoses from the engine and flush backwards with the garden hose!! You need PRESSURE!! Another way is to revers the hoses, which will work, with the addition of spline adaptors, but you will need to run the heator for several days to heat it up and flush it out good. Then once it is free and flowing, flush entire system and replace with clean water and antifreeze!!
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post #3 of 6 Old 09-15-2008, 09:18 AM Thread Starter
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thanks for the advice...i am going to try that this weekend. Did you have the same problem with the blower...That when accelerating the vents will switch from head, feet, to the defrost only?
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post #4 of 6 Old 09-15-2008, 09:24 AM
Jerry Bransford
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2004 TJ Wrangler 
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Location: Escondido, California
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Your engine produces less vacuum when you accelerate, and it is vacuum that controls much of your HVAC system. So it sounds like you have a vacuum leak since there's not enough vacuum to keep the HVAC working during acceleration. I'd look for a disconnected, split, or broken vacuum hose, or perhaps a broken vacuum manifold (a fancy word for something that distributes vacuum from one hose to several others).

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post #5 of 6 Old 09-15-2008, 10:11 AM
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1997 TJ Wrangler 
Join Date: Mar 2003
Location: Longview Wa
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one test the service manual suggests for your water pump is to turn on your heater.
it may be a sign of something else but lack of heat also points to failing water pump.

not saying yours is kaput, but it is a good thing to know if the signs are present.

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post #6 of 6 Old 09-20-2008, 10:19 PM Thread Starter
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I just flushed my heater and that solved the problem! thanx for all the advice and suggestions
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