Only Luke Warm Heat At Best - JeepForum.com
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post #1 of 10 Old 05-12-2021, 03:20 PM Thread Starter
Keekers McGrew
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Only Luke Warm Heat At Best

Hello Folks,
This is my very first post on this forum, so please forgive me if I'm posting this in the wrong place.

I have a 1999 Jeep Cherokee Sport with the 4.0 L engine, and it currently has 135k miles on it. It still runs great, but just this last February, when it was 15 degrees outside, I noticed that my heater would not blow air any hotter than luke warm. The first thing I thought was the heater core was hosed and needed to be replaced. But after doing some research it seems like I only needed to flush out the heater core. I saw a few excellent videos on how to do that, but I didn't want to mess around outdoors with temps like that. So I called the Firestone mechanic in my neighborhood, since they were the only people open. Where I live, weather like this shuts the whole town down. The Firestone mechanic said that for $35.00 he would give the heating and cooling system a good look over before he went ahead and did the heater core flush. I agreed, and when they were done they said they saw a leak at the water pump gasket. They then recommended that they replace the entire water pump, along with the gasket, and then flush the entire cooling system. I also figured they may as well change the t-stat too. They agreed to do all this for $900.00, so I decided I would do it myself.
This last weekend I installed a new water pump, t-stat, t-stat housing, thermo sensor, the upper and lower rad hoses and also the coolant over flow reservoir. When I was done I flushed the entire cooling system. Then I filled everything back up, burped the system and let it run for approximately 45 mins to make sure there was no air in the system. I also let the heat run too, and it still never got hot and the Jeep never got to 180 degrees. I did put a 160 degree t-stat in, and maybe that was a mistake. But after all that, I took my Jeep out for a cruise with the heater turned all the way up, and still no hot air and the Jeep doesn't get past 180 degrees.
Tonight, when I go home I will check the hoses going to the heater core and radiator and make sure they're all at a reasonable running temp. I'm also going to check to make sure the coolant in the radiator is at the right level. If all that is fine then I'm not sure what to check next. I would appreciate it if anyone can give me some clues or suggestions. The good news is that I really don't need heat any more, but I want my rig to work like it's supposed to.
Thanks to all who read this, and again, if I'm posting in the wrong place please accept my apologies. Happy Jeeping all., :-)

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post #2 of 10 Old 05-12-2021, 04:12 PM
CJ7-Tim
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The specified thermostat for the 4.0L is 195*. The dashboard temperature gauge should indicate approximately 190*-210*. Using too low a thermostat can cause the engine computer to never switch into closed loop and your gas mpg's will be really bad.

Install the correct thermostat and see if the heat improves. If not, the heater core is likely clogged and may require multiple flushes with a radtior flush product, or even may need replacement.

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post #3 of 10 Old 05-12-2021, 05:59 PM
axlaxl
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Just curious when you say you flushed the entire system, did you specifically BACK FLUSH the heater core?

Also, turn heat on full when up to operating temp and feel both hoses going to the core, is one hot and one noticeably cooler?

And yes do what Tim says and rip out that 160f tstat.
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post #4 of 10 Old 05-13-2021, 10:39 AM
superj
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i would take the two hoses to the heater core off and put your yard hose up to them and run the water back and forth through them till its flowing clear and strong. than you know that sucker is flushed. if it gets you heat, good to go.

if not, maybe you have a blend door issue also? but hopefully its the heater core not being completely flushed since its warm weather and you are getting cooler temps than you should be.

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post #5 of 10 Old 05-13-2021, 12:07 PM Thread Starter
Keekers McGrew
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Appreciate the great suggestions. I wasn’t sure about the t-stat I put in. I figured if it was the wrong one I can always swap it out. I would much rather throw away $5.00 to $10.00 for another t-star and gasket any day over putting in a new heater core. I’ll put the new t-stat in this weekend.
As far as the back flush, what I did was pull off both heater core hoses, and then I ran water through the top hose and it drained out of the bottom. Then I ran water through the bottom and it came out the top. I went back and forth like this until the water was clear. The water never really gushed out because I didn’t have the hose on very high. I read somewhere that if you put too much water pressure into the heater core you can cause significant damage. I would say that the water came out as fast as I put it in, so I think I’m good there. If the problem still persists I may do it again. Hope I did it correctly in the first place. Lol
When I felt the heater core hoses both were hot, and the top one was a bit hotter than the bottom hose.
Thanks again, and I’ll keep you all posted.
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post #6 of 10 Old 05-13-2021, 12:28 PM
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you did it right. no problems there than. so if the hoses are hot than maybe the core has debris blocking the air from going through it so you are getting low heat transfer and cool air at the vent?

i don't remember how the heater core sits but maybe some leaves or dirt has fallen into it from the fresh air vent and its blocking it?

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post #7 of 10 Old 05-16-2021, 03:31 PM
robdiddy
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My luke warm heat situation got fixed by a radiator flush, but now Im posting about devastating over heating and coolant leaks. Be careful may god watch over your XJ and not have your suffer the same fate as mine.

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post #8 of 10 Old 05-16-2021, 03:37 PM
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Quote:
Originally Posted by superj View Post
you did it right. no problems there than. so if the hoses are hot than maybe the core has debris blocking the air from going through it so you are getting low heat transfer and cool air at the vent?

i don't remember how the heater core sits but maybe some leaves or dirt has fallen into it from the fresh air vent and its blocking it?
If mine started with this same type of stuff... and then i began to over heat and lose antifreeze wouldnt a clog in my heater core seem like a logical thing to look for?

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post #9 of 10 Old 05-17-2021, 10:25 AM
superj
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a clog in the heater core won't make it overheat and lose coolant though.

does your exhaust smell sweet, like coolant, when its running, @robdiddy ? that's a good sign you are getting coolant into the combustion chamber which could be a headgasket.
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the xj is the only jeep left in the driveway
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post #10 of 10 Old 05-17-2021, 01:25 PM
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Also check your Oil For Antifreeze... Cloudy milky color
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