OK guys,
99 Cherokee sport, made in 10/98 135K miles. Always runs at 210 degrees.
Heat has been only lukewarm since I bought it 30 days ago.
I searched and read as many posts as I could find about this issue.
I checked the flapper door and the stepper motor, the motor works as it should and when the door is at the end of it's travel, turning it by hand does not make it move more or "flex" any. The stop is solid.
I have flushed the heater core forward and backward, over and over and over using a garden hose. The first few flushes produced the most crap, the last few produced just clear water. The water comes out just as fast as it goes in. Then I flushed out the overflow bottle, whole lotta mud in it. I then replaced the water pump, the theromstat, and the coolant.
Still lukewarm heat. Both heater hoses are hot when the engine is up to temp.
Is it POSSIBLE that the heater core tubes are still plugged and the water from the hose kinda just goes across the end of the core and out the other pipe?

Ken R

 

When the engine is at 210 degress, are both of the heater core hoses hot?

 

Yes, They both get hot. I don't want to hold on to them for too long........

 

Did you also flush the motor and radiator? Maybe more stuff ended up in the heater core. You could try flushing the core again. But if both hoses are as hot as the radiator hoses then maybe there is an issue with the blend door.

 

Yes... All the lower tubes could still be plugged and just a few upper tubes are flowing. Not enough to do much good. There is a risk you will have to judge with what I am about to suggest. Since it is almost to the point of needing replacement anyways, if it were mine I would undo both heater hoses and gently blow backwards through it a couple times with my index and thumb wrapped around a blow gun with air. Just short easy bursts and then rinse it again backwards with the water hose.

From what you describe here with how much junk there was in it, I would bet there is still more that only air can blow loose in those tubes. But depending on how rotten it is, it could burst the core if you hit it too hard for too long. Your call on this one but I have done this countless times as a last resort to unplug a core with success.

 

Does the air come out of the vents at full speed? Does the air smell bad? There could be a mouse nest in there blocking the airflow if you answered yes to those two questions

 

SAME issues with my '99 too! I flushed the core SEVERAL times and use CLR twice. I have better heat but it's still not gonna work when it hits -10F here in a month or so.

Looks like I will be replacing a heater core one of these weekends.

 

Watch THIS video for complete system flush. It's extremely informative, and in my opinion most complete flushing guide I have seen

 

Waynerd, I didn't flush the block and rad, It just didn't occur to me to do that. Doh!

Bugout, I chose not to push the water with air, as I have no want to have to replace the heater core. I might tho, if the heat stays crummy.

Trailer, Full air flow. No mouse nest smell or coolant smell. Blower fan moves a lot of air.

SirCyber, Mine was nowhere near as bad as that poor Jeep in the video. I will do that kind of flush if I need to reflush this thing again.

 

When I replaced everything,(Waterpump, thermostat, rad cap,coolant) I pressure tested the system and it holds 15lbs for as long as I want it to sit. However.......... when the motor is running, it creates no pressure. None. It idled for about 30-45 minutes and the heater hoses were freakin hot, the top hose was hot and not a drip of leakage to be seen. The new rad cap was warm to the touch and could be removed without ANY hissing or pressure releasing. Whisky Tango Foxtrot!! I pressure tested the system again and it holds pressure fine and tested the new cap. It will hold 10lbs of pressure but will leak down from higher. It does not seem to seal in the radiator neck though. I will exchange it for another one.
The saga continues.

 

The part of the video that might help the most was the heater core, but here's a thought. If the t-stat is stuck could it cause this type of issue? Do you still have the heater control valve? I know those can be faulty as well. I bypassed it in my '95 after it blew chunks of plastic and coolant all over my engine... Right before we went out on some ORV trails. Guess it was a good thing that happened before but dang sucked being lead man right out the gate with a failure... But I digress... T-stat, heater control valve, good heater core flush.

 

Cyber, I don't think the 99's have that control valve.
I exchanged the Rad cap for another one. The system now makes pressure. At highway speeds, the warm air gets much warmer than before, but it is 45 degrees right now. I think I will look into the blend door thing next.

 

Ahh ok. Lol well I only speak from experience, and don't have experience in all things jeep yet. Good to know they did away with that cheap hunk of junk in later models! I don't have experience with the blend door thing either, so I guess now I'm on the sidelines watching and learning. Good luck!

 

Have you checked your gauge against a temp gun yet? I once went through two brand new out of the box thermostats before finding the third actually worked.

 

I haven't even started the Cherokee since my last post. I drove it yesterday and the heat was warm enough to be acceptable. However, it was 50 degrees outside. When time allowes, I will continue the research and make it better.

Bugout, Not yet. I need to buy one. I will say this tho, if the air from the heater box was even 2/3rds as hot as the heater hoses themselves, I would never complain about the heat.
Ken R