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Old February 22nd, 2013, 08:28 PM   #1
Marion3
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Default Luke warm heat

I read the thread below with the blower motor resistor as the fix but im curious as to what everybody thinks here


Bought a 99 xj a few days ago and starting to get things squared away with it.

At idle the heater blows cold, cruising down the road at 55 heat is luke warm.

Replaced the thermostat today with no luck.
Heater hoses are hot and do not collapse at rpm's
After a 15 minute drive I stopped and checked coolant level which is good,but radiator cap was cold and I opened without any pressure against it.

If it matters my blend door takes a few seconds to switch from floor to vent to defrost,ect


What gives?????
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Old February 22nd, 2013, 08:29 PM   #2
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Mainly I'm stumped as to why my temp gauge is dead on with no overheating what so ever but yet my radiator cap is cold and no pressure against it
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Old March 4th, 2013, 07:27 AM   #3
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Sound like a clog in the system some where. Dose the temp guage work, your referance to dead makes me think not. I'd get a new sensor if it were not, it would make diagnosing issue easier. 15 min, seems long enough to bring it to opperating temp, but its been pretty cold too.
Have you flushed the system yet?
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Old March 4th, 2013, 07:29 AM   #4
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My daughters did this and it ended up being just a bad radiator cap
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Old March 15th, 2013, 04:48 AM   #5
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My 2000 did the same thing, took both heater hoses off the engine and pour CLR in it let it sit for about 15 min. and then flushed it out, flush it into a plastic jug to see if you get any crud out of it. may have to do it a couple of times. Good Luck
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Old March 15th, 2013, 10:57 AM   #6
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Water pump could be bad and it sounds like you might have a leak?

I just replaced a radiator with both hoses, water pump and thermostat on a 92 Cherokee and the heat worked much better after. I think there was an air pocket in the heater core. I used a vacuum filler for the coolant. Also the heater control valve is a common part to break and leak from.

The radiator was leaking slowly and I figured it would be good to replace all the cooling system wearable parts at the same time.
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Old March 18th, 2013, 01:19 PM   #7
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Ended up being a clogged heater core. Just blew it out with compressed Air and it works decent now. I read about the clr and I'll have to try that
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Old April 9th, 2014, 07:26 AM   #8
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I got a TJ doing the exact same thing right now, just bought it a few weeks back. Temp sits at 210 but top heater hose is hot the bottom one is not. :-(
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Old April 9th, 2014, 07:44 AM   #9
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Quote:
Originally Posted by Hooperdog View Post
I got a TJ doing the exact same thing right now, just bought it a few weeks back. Temp sits at 210 but top heater hose is hot the bottom one is not. :-(
That is an easy fix. Back flush that heater core. Only takes about 15 minutes. I normally just use a garden hose and an adapter.

My yukon with 130k had some freaky shit pour out of it. Couldn't believe the heat after I cleaned that out.
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Old April 9th, 2014, 11:30 PM   #10
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Quote:
Originally Posted by clarkstoncracker View Post
That is an easy fix. Back flush that heater core. Only takes about 15 minutes. I normally just use a garden hose and an adapter.

My yukon with 130k had some freaky shit pour out of it. Couldn't believe the heat after I cleaned that out.
That's a good, cheap first step, but doesn't always work. Sometimes the heater core is just too far gone. Always worth a try though before you pull a dash.
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Old April 10th, 2014, 12:13 AM   #11
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Had same issue on my tj. Ended up being clogged heater core. Find the outlet line to heater core and hook air gun to it. Remove inlet line and connect it to a gallon jug. Spray the air through in spurts. Some nasty stuff will come out and then heat should work again.
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Old April 10th, 2014, 06:25 AM   #12
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I wouldn't use compressed air, use a garden hose and don't use full pressure until it starts flowing free. Go both ways a few times.

I have had a few TJs that were getting up to full temp and still had poor heat. The heater core was plugged on the outside from leaves and junk. Pull the blower motor out and stick a shop vac in there.
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Old April 10th, 2014, 06:34 AM   #13
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Thanks, dropped it of to Big B for the lift install and axle swap, he's going to flush the heater too, I'll have to check the blower motor when I get it back, (unless he does that too) hint, hint.. lol
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Old April 13th, 2014, 09:41 PM   #14
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Flushed it, didn't see anything come out, put new thermostat in and all new fluid, seems to work good. ?? Maybe thermostat was causing it?
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Old April 13th, 2014, 10:33 PM   #15
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Heater core plugged, flushing sometimes helps, if half the core is plugged you will only get half the heat flow across it, hence the Luke warm heat, both heater hoses will be hot because you still have some coolant flowing threw the top few holes, I've flushed many at work, some produced heat others needed to be replaced, we even cut open the old heater core and see them packed halfway up with junk

We even use acid as a last resort in a 50/50 mix with water, let it sit in the heater core for a few mins then flush with water, blow with compresses air, back flush with water, then back blow with compressed air
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