Hello, im fairly new to the forum but have search everywhere and cant find an answer to my question.
I have a 97 jeep wrangler 4.0. I bought it 3 years ago and it never had heat. I first replaced the radiator because the owner before had it sitting outside with no coolant and every rusted. I replaced radiator and got warm heat. I did a full flush of the block, heater core and rust came out but flushed until it was clean. I also replaced the water pump and thermostat. I fixed the vacuum actuator arms so everything is working properly in the heater box. I just replaced the heater core about 3 weeks ago. made sure the blend door has no cracks and it works properly. while having the heatercore out I drained all coolant flushed the block and added fresh coolant to the system and then after reinstalling the heater core properly bleed the system. I now have warm heat, not hot. it was just 10 degrees outside and my heater is barley warm. What else is there to check. or what else can I do?!. I have a electric fan that is on all the time. does that maybe have something to do with it? I have a thermostat that is 195 but my jeep seems to run around 180 190..does a electric fan make my jeep run cool that it wont be hot air? and my heater hoses going to heater core are hot to the touch, with the one being alittle cooler.

I checked vaccum lines.
blend door
coolant and flushed everything multiple times
all actuator arms work. no leaks in my ducts all blow good power air out of them
thermostat. just stock setting I think 195
waterpump.
radiator and heater core.
everything is new I don't understand.

why do I not have hot heat is a total mystery to me. any input would help a ton

My only thought is that there is something restricting flow to the heater core. Could be a large rust deposit that did not flush out of the block

How do you know the Jeep is running that cold?
With a 195 t-stat it should be running at 190-200
(note: this is not the problem with your heater, this is a separate problem).

Prestone used to make a cleaner P/N AS100 Heavy Duty Cooling System Cleaner
It is not made anymore (EPA) but these are the components. This was sold up untill 10 years ago or so
and it really worked well
9 dry oz of Oxalic Acid (DAP Wood Bleach)
2 dry oz of Sodium Carbonate (Arm & Hammer Super Washing Soda)
Remove the thermostate and drain the old coolant
Refill with the Oxalic acid and water. Run for 20 to 30 min.
Drain and flust until clear
Refill with the sodium carbonate to netralise the acid and run for 10 min
Drain and flush untill clear and refill with antifreeze.
Disclaimer
Use at your own risk
Oxalic acid is a poisin read up on it and follow saftey precaution.
Dispose of all waist properly
If you have failing head gaskets of freezout plugs you will find out.

It would be worthwhile to check the heater hose nipple on the thermostat housing and the pipe on the water pump for obstructions.

Is the valve that flows hot water to the heater core opening all the way?

HEATER PERFORMANCE
Before performing the following tests, refer to
Group 7 - Cooling System for the procedures to check
the radiator coolant level, serpentine drive belt tension,
radiator air flow and the radiator fan operation.
Also be certain that the accessory vacuum supply
line is connected at the engine intake manifold.

MAXIMUM HEATER OUTPUT
Engine coolant is delivered to the heater core
through two heater hoses. With the engine idling at
normal operating temperature, set the temperature
control knob in the full hot position, the mode control
switch knob in the floor heat position, and the blower
motor switch knob in the highest speed position.
Using a test thermometer, check the temperature of
the air being discharged at the heater-A/C housing
floor outlets. Compare the test thermometer reading
to the Temperature Reference chart.
If the floor outlet air temperature is too low, refer
to Group 7 - Cooling System to check the engine coolant
temperature specifications. Both of the heater
hoses should be hot to the touch. The coolant return
heater hose should be slightly cooler than the coolant
supply heater hose. If the return hose is much cooler
than the supply hose, locate and repair the engine
coolant flow obstruction in the cooling system. Refer
to Group 7 - Cooling System for the procedures.

OBSTRUCTED COOLANT FLOW
Possible locations or causes of obstructed coolant flow:
† Pinched or kinked heater hoses.
† Improper heater hose routing.
† Plugged heater hoses or supply and return ports
at the cooling system connections.
† A plugged heater core.
If proper coolant flow through the cooling system is
verified, and heater outlet air temperature is still
low, a mechanical problem may exist.

MECHANICAL PROBLEMS
Possible locations or causes of insufficient heat:
† An obstructed cowl air intake.
† Obstructed heater system outlets.
† A blend-air door not functioning properly.

TEMPERATURE CONTROL
If the heater outlet air temperature cannot be
adjusted with the temperature control knob on the heater-
A/C control panel, the following could require service:
† The heater-A/C control.
† The temperature control cable.
† The blend-air door.
† Improper engine coolant temperature.



Temperature Reference
Ambient Air Temperature 15.5° C
(60° F)
21.1° C
(70° F)
26.6° C
(80° F)
32.2° C
(90° F)
Minimum Air Temperature at Floor
Outlet
62.2° C
(144° F)
63.8° C
(147° F)
65.5° C
(150° F)
67.2° C
(153° F)

+1 on this keep in mind the offending piece may only cause a problem when there is flow in the system.

I have thought this too, its possible. I will say, I replaced radiator, when I did I flushed my (old) heater core out, block, and everything out with a just a napa brand cleaner they sold. don't remember the name. but the rust chunks that came out where big. when I flushed this last time with my heater core out. so I took my heater core hoses and ran water threw the block and out the other hose then switch and drained my radiator and flushed that. and the water was slightly discolored not as bad as I thought tho. not a single rust pieace came out. but like someone said there could be a big chunk stuck somewhere I cant find. thank you for your response!

thanks for all the info! the only thing im confused is the valve your talking about for the heater core? where is that located? mine just has two hoses one in and one out obviously but I didn't see any valve for it? any pictures or explain where a valve is at?

I don't think there is any valve.

The TJ heater system does not employ a heater valve. Heat is regulated via the blend door.

???

Try a new 195° t-stat

Be sure you have a 195° MOPAR or Stant thermostat in there.

In your climate, the constantly running electric fan is overcooling the coolant in the radiator as well. Either put a thermostat control on it, or block part of the radiator with cardboard, etc, like the big rigs do to get it up to temp.

Your temp gauge should be in 210 range at full operating temp.

Yeah, its sounds like the T-Stat is stuck in the open position.

yea my fan is wired into my ignition so as soon as I turn my key on the fan runs wide open all the time. that's why I was wondering if that had anything to do with it. Im going to replace the thermostat once again to try to see what happens just because its quick and simple.

I wish I could explain where my needle for my temp gauge is at. I don't have a picture to show but if your familiar with the dial it goes 100 then a line then 210 and its in between the the line and 210 maybe a touch more then half way in between the line and 210.

thank you for your input!

Most of them I have seen run about a needle's width below 210 when up to operating temp.

Sounds like you might have a fail safe thermostat (you don't want this as they tend to fail open).

Also, your electric fan should not be on all the time, only once the engine is warmed up to a certain temp.

Looks like your t-stat is stuck open,
For my `04 TJ, here's what the gauge reads (when compared to an OBDII reader)

My Jeep operates at the 200° line.

yea mine is deffinatly below that 195 degree line. not by much but for sure below. I will replace thermostat and see where that gets me.

thanks for that photo it was perfect

Put a piece of cardboard in front of your radiator to obstruct the airflow. Then see if it warms up some. (Don't cover your radiator completely, only 50%-75%.)

To test the theory that a constantly running electric fan is the problem, disconnect it and test drive it. When the vehicle is in motion, it should cool sufficiently with no fan at all. Keep an eye on your temp gauge just in case, but if your heat suddenly gets better, you have your answer. I really don't think the electric fan is the problem since the any stock mechanical fan runs all the time too and overcooling hasn't been a problem.

Deleted.

Since nobody else suggested this put your hand on each heater hose near the connection to the core when the engine is up to temperature and confirm that each hose is hot to the touch, not warm or fairly hot.

Do this after replacing the stat to confirm proper flow.

I do heating and AC work commercially and design engineers often use a 20 degree drop across coils so I would expect if the system was working properly the input temp to be engine temp and the temp coming out of the heater core to be about 20 degrees less if the heat is being carried away into the interior by the air flow. If the temp is the same in and out it means you have no air flow. I suspect something with the mixing box if the temps are the same. Can you manually open and close the damper? If you can you can likely hear it thump as you move it one way or the other. Is the shaft striped on the damper. In putting the thing back together is the damper binding? Is the pneumatic actuator diaphragm broken? Are the controls actually pulling a vacuum on the damper? A mighty mite hand held vacume pump with gauge is very helpful with these things. Are hoses connected as they should be? See if you can manually work the dampers and get heat. Bob Harrison

Oh and get a thermostat or factory set up for the fan.

Have you removed the heater fan? my 97 was so full of pine needles, leaves and trash that it had clogged the heater coil so bad it would not heat. I had to remove the battery, battery tray and a few other things then just took it out and used my shop vac to get it out. I had to use a small screw driver and reach in the hole and pry some of the gunk out. PO had parked jeep under pine trees all the time he had it. good luck

I have been working on mine for 2 days now,trying to carefully check all the easy stuff that has been written in on this forum. I was getting close to doing the cut to get to the blend flap. I have already flushed my heater core twice and stuff did come out. Last night I seen a youtube video where a guy reversed the flush. WOW a lot more stuff came out and I now have good heat!! May not be your problem but only took 15min. Try the easy stuff first. Also the heat going into top of heater core was 160F out the bottom only 110F a good sign that I didnt have good flow. Now its about the same top and bottom hose.

210 is the more common temperature when running the correct 195 degree thermostat. I would only expect 190-200 degrees if an incorrect 180-degree thermostat was run

He probably has solved his problem in the year since this thread died

Heater control valve