How To: Heater core replacement

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Trainmaster

Member
Joined
Jul 4, 2019
Messages
33
Reaction score
12
I had pumped the Delco sealing tablets through the heater core as was recommended and it worked great -- for a month. Thirty-seven days has gone by and the small leak is back. Looks like I'll be pulling the dash.
 

LibertyTC

Well-Known Member
Staff member
Moderator
Joined
Oct 24, 2008
Messages
9,178
Reaction score
1,825
Location
B.C. Canada
Delco sealing tabs/stop leak is a temporary solution and not really recommended.
If you need a new Mopar thermostat or new hoses, now would be a good time to replace them.
With a new heater core installed, make sure you flush the entire system well afterwards.
Then install the the correct Mopar HOAT or Zerex G-05 coolant.
 
Joined
May 26, 2020
Messages
76
Reaction score
27
Location
Squamish, BC, Canada
I tried the same hack to externally pump Rislone Liquid Aluminum through the leaking heater core but to no avail. I tried 20min with the recommended concentration and afterward 20min with double concentration. Zero impact. I had the cabin fan going as well to move air over it, but it could also be that this particular product needs heat to activate. It does appear that my leak is quite bad so I was never overly optimistic. Probably going to try once more with a different product at high concentration.

The tabs must work by mechanical accumulation in the system hole/crack. Whereas I believe some liquid products are heat and/or oxygen activated. The manufacturers dont seem to state the active mechanism at all.

The replacement job sounds like a nightmare to me but some comments in this tread have given me hope. Thanks!
 

Big Al

Let's get Cracken
Joined
Jul 26, 2020
Messages
178
Reaction score
91
Location
Vancouver,B.C.
Just finshed installing a new heater core, went for a cruise and it feels I went to hell and back that the KJ is so warm. Picked the Jeep up in 2020 and I always knew that I needed a new heater core.
Once I removed it today, I went and pulled the top plastic manifold off of the old heater core to see what it looks like inside.
At first glance, it looked like there was pink jelly in numerous tubes, then I thought why don't I try to fill up the 12 U tubes with a water bottle and see how many are plugged. Well I had flow out of 3 of the 12 tubes.
That makes the core 75% plugged.
I had a bit of heat on setting 2 and no heat on setting 3 and 4 for almost 4 years.
I also tried 3 times to flush it out, but the solution I used just went to the path of the least resisitance through the 3 tubes.
If you got no heat, put a new heater core in, I did it without evacuating the A/C, it was tight and I made no modifications to the new heater core.
Took most of it apart on Friday night and then went at her Saturday morning.
First time doing a heater core and now I'm an expert. JK.
10 hours from start to finish.
Miller time now.
 

KJowner

Full Access Member
Joined
Oct 20, 2022
Messages
1,386
Reaction score
788
Location
Uk
Bet someone put one of the 'magic' stop leak products in it, they always cause more problems than they fix.
 
Joined
May 26, 2020
Messages
76
Reaction score
27
Location
Squamish, BC, Canada
I also replacement my heater core this weekend. Definitely a big job! I think it took me a little over 10h but overall it wasn't as frustrating as I feared it might be. Every youtube example is slightly different it seems.

My approach summary:
- partially drained the cooling system from the radiator petcock.
- Evacuated the AC and pulled those lines from the engine bay. (I'm not certain this was necessary but I'm also surprised to hear that @Big Al (post above) was able to pull the HVAC box back far enough to fully access the heater core while the AC lines were still attached. That did not seem possible to me but aparrently there is a way...)
- Left the steering wheel and airbags in place. I did loosed the 2 vertical black starnuts which hold the wheel-adjustment-limiting-bracket to the column, just to let the wheel drop an extra inch. Those same bolts also prohibit the plastic dash from moving forward enough.
- The only electrical connection I touched at all was the passenger side dash tweeter/speaker.
- I took the dash instrument panel out (4 screws) but left it connected electrically.
- Didn't touch any pneumatic/vacuum devices/lines other than the blend actuator line which sneeks through the firewall alongside the AC lines.
- Used a ratchet strap from the rear passenger. Didn't need to go crazy on it.
- Ultimately I had enough clearance to easily reach behind and pull the core straight out without doing anything weird. I could even look down into the mounting slot and see the coolant down there to clean it up.
- I haven't tested my old core yet but it visually looks to be in a terrible state with old and new glycol stuck all over it.
- New core from Four Seasons was $42CAD+30CAD shipping to BC on RockAuto.
- Refilled the cooling system and immediately bled it from the hex port near the upper radiator
- Fortunately, and somewhat amazingly, everything works perfectly now. Heat is better than ever.

Tips:
- there are two bolts behind the radio/AC control panel which firmly connect the dash to the HVAC box. I found that separating the dash from the chassis and firewall was one thing, but separating the HVAC box from the dash was a separate thing. You need both to get ample clearance.
- dont try to skimp on removing plastic panels.
- definitely get yourself one of those reverse-pliar sets which pull apart when sqeezed. They are made for removing auto panel pressfits and work like a charm, dramatically reducing the chance of things breaking. Cheap on Amazon.
- have a long extension piece to your 1/4" ratchet with a deep 10mm socket. Some of those were hard or impossible to get a 1/2" socket set on due to the larger diameter.
- a couple of the 10mm bolts require a deep socket. None of the 13mm bolts did.
- Most of the plastic panel screws are the same, 7mm with a phillips #2 inside.
- being in a heated garage really helps the compliance (and non breakability) of the interior plastic panels.
- when you go to push the whole dash+box back into place, dont forget about the AC condensate spout! Its that 3" bent rubber hose which sticks through the firewall down low.
- If you have any known naggling dash area creaking or vibrating offroad, now is the time apply some lubrication and electrical tape.
- If anyone sends me a DM with further questions I'll try my best to help.

Mechanic cost?
- My trusted mechanic quoted me $1500 but couldn't do it until early Feb. They were also very unexcited about the task.
- The second most reputable autoshop in town quoted me $1900 but when asked to commit retracted entirely, saying its too risky of a job for them.
- A lesser trusted mechanic in town declined to offer any price, saying its a terrible and uncontrollable job.
- The Crystler dealership in town quoted $2300 "If everything goes absolutely perfect, which it wont." And could do in early January.
- Nuts. Just nuts! I'm an idiot and still figured it out in reasonable timeframe.
 

derekj

Full Access Member
Joined
Jul 4, 2013
Messages
235
Reaction score
352
Location
Powell River, BC
Mechanic cost?
- My trusted mechanic quoted me $1500 but couldn't do it until early Feb. They were also very unexcited about the task.
- The second most reputable autoshop in town quoted me $1900 but when asked to commit retracted entirely, saying its too risky of a job for them.
- A lesser trusted mechanic in town declined to offer any price, saying its a terrible and uncontrollable job.
- The Crystler dealership in town quoted $2300 "If everything goes absolutely perfect, which it wont." And could do in early January.
- Nuts. Just nuts! I'm an idiot and still figured it out in reasonable timeframe.
What shops did you get quotes from? I worked at DHM for 10 years before I moved to Powell River a few years back. Seems odd that shops would turn down work....
 
Joined
May 26, 2020
Messages
76
Reaction score
27
Location
Squamish, BC, Canada
What shops did you get quotes from? I worked at DHM for 10 years before I moved to Powell River a few years back. Seems odd that shops would turn down work....
I was surprised also. What they tell me is that mechanics are in such critically short supply that shops are basically fending off work.
 
Top