Rednroll

Definitely going to cut it open. However, I think the flush may have worked where I may not see any deposits. We'll see, I think I just let it run too hot and for too long. I'm guessing the joints of the tubes which connect to the core, likely sprung a leak. I'm waiting for the replacement core to arrive in the mail and I bypassed my heater core so I can still drive in the mean time, but with no interior heat. If it warms up today, I'm going to work on pulling out the old HC.

ronjenx

This is a pretty good thread. I thought I would add some data I collected today from my 2008 JKU.

Ambient temperature: 45°F
Coolant temperature: 195°F (engine idling)

Temperatures at various modes with max temperature selected, recirculate off:

Set for Dash vents only...
center outlets with fan high:170°F; with fan low: 185°F
left and right outlets with fan high: 160°F; with fan low: 180°F

Set for foot only...
left and right with fan high: 140°F; didn't check with fan low.

Set for defrost only...
With fan high:155°F; with fan low: 175°F

Temperature at center dash vents, with temp selector at mid-point, mode set to dash only:
with fan high: 110°F; with fan low: 100°F

Note that with max temp, a slower fan speed raised the temperature output, and with mid temp, a slower fan speed lowered the temp.

Rednroll

Great info, thanks for posting. I'm hoping to see similar results once I get this heater core replaced. It's been a long time struggle trying to get back to having good working heat.

The background reasons I decided to take my vent measurements with the settings I did is due to a recent A/C problem I had on my wife's Jeep Renegade vehicle where the dealer measuring procedure is as follows.
Fan=LOW
Duct selection=Vents
Temp dial=(full cool), switched to (full heat for heater).
Recirculate=OFF

To determine if your A/C is working within spec, it should read at least 30F below the outside ambient temp.

So I just use a similar measurement for the heater, where there I know the coolant running through the heater core is typically in the 180F-200F temp range, so expect to see something which is 20-30deg below that typical engine coolant temp blowing from the vents.

Rednroll

I got the old heater core out, new one arrived in the mail today.

The leak was a hole in the bottom tube right next to the core. The bottom tube fitting where it attaches to the core was leaking as well, which seems to be a common failure for some reason.

I'll cut this core open once I finish getting the new one installed. I decided to put JB Weld around both of those tube fittings where they attach to the core on the new one. It seems pretty weak.

Rednroll

Ok, I got the heater core replaced. Now this is the heat I remember feeling coming from the vents when it was new.

The funny thing, I learned my HF digital thermometer starts acting funny, shows an "E" for error "temp too high" and craps out once you start exceeding 175deg F. It crapped out on me for the center and passenger side vents. So those vents are now hitting close to 180 deg F.

Temp measurements with new heater core.

Outside temp 43F


HVAC controls Measurement Settings:
Fan Blower Motor=LOW(Min)
Re-Circulate= OFF
Temp Dial= Max Heat
Vent Selector= Front Vents only

Driver side vent 155.5F


Center vent 173.7F


Passenger vent 178.8F (display is starting to go out on thermometer, so that's why it's hard to read)

Mr.T

Rednroll

Here is the cross sectional dissection of my old heater core. Mine wasn't clogged with hard calcium deposits. It was more like clothes dryer lint fabric material. It was clogged up more on the driver side.

Top full view


Bottom full view



Top zoomed


Bottom zoomed

ronjenx

I haven't had any heater core problems, but if I do, I won't be dreading changing it.
Thanks for posting the repair. I was glad to see the removed brace go back in, too.

Rednroll

It's definitely the way to go, it beats the heck out of removing your center console so you can remove the entire dash, and then additionally removing your battery and tray to be able to reach the HC hose connections.

I posted this in B.Law's thread and will re-post here in regards to the cage repair.

As an additional note for anyone doing this heater core swap method. I think where the cage repair is most important is when you go to fasten your glove box trim back together. There are a total of (5) 7mm screws that hold that trim down. (4) of those screws are the frame for your glove box where (2) of the trim fastening points are located on that cage section that you have to cut out. I used ratchet straps to pull that trim out of the way so I had room to work. Well, having it pulled like that bent the trim out of proper alignment and being able to fasten the trim back to those 2 anchor points on the removed section of the cage, pulled the trim back into alignment so it looked right and your glove box opens/closes properly. I would have to think without doing the cage repair, you may run into problems where your glove box may not open/close properly when put all back together.

An additional tip on the cage repair. There is a bracket on that cage section that I cut out, that holds the cage to the dash. There's a single 8mm bolt that holds that cage to the dash. B.Law cut to the left of that bracket so the mounting bracket was still in place. I cut to the right of that bracket, so the bracket came out with the cage section that was removed. I think cutting to the right of that bracket is important, since that will assure that those (2) trim mounting holes that are located on the cut out cage section, are still properly aligned with the trim mounting holes, so everything is properly aligned during the trim re-assembly.

Here's a pic to better show what I'm describing.


Heater core replacement install


Cage repair, using 1/2in C-Channel from Home Depot and 3/16in rivets.

Rednroll

While I had this all apart, I was able to determine why I have been having trouble getting my vent selector to lock into the Defrost position. That large white gear assembly is the vent selector actuator mechanism. I sprayed that large white gear, all the slide points, and cable down with some white lithium grease and now my vent selector is back to working and easily locks into the defrost position.


I also put a small zip tie on the post that the cable loop slips around on that white gear assembly. There's nothing that prevents that cable from slipping off of that post, and when switching to the defrost position, and it wasn't locking into that selector position the cable was pushing outward towards the end of that post. So by adding the zip tie, that now ensures the cable doesn't slip off the post and additionally when the cable hits the zip tie it stops the cable from slipping outward and provides additional leverage to ensure the cable continues to push the gear assembly forward.




After I got this all done, I just drove around in my Jeep with the heat and defroster's blasting, windows rolled up and sweating my arse off with a big grin on my face. Having good working heat in your Jeep makes driving it so much more enjoyable. I'm now ready for the snow, and go hit those snow trails without freezing inside my Jeep.