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Discussion Starter · #1 ·
Here’s a fun one.

So I did a heater core flush this week, using a technique I read here; use a submersible pump in a bucket of water with rad cleaner and let the pump run for a few days. Did it each way (in the top, out the bottom then in the bottom and out the top). I had full flow almost instantly. Then after 48 hours of flushing I blew some compressed air through just to be sure, no restrictions.

Didn’t get too much debris out, but when I put it all back together and bled I went for a drive and I had heat! Win, right?

No.

I came out a few hours later to do another bleed for good measure and there’s coolant under the Jeep. Thought it was one of the clamps on the heater hose on the firewall so I installed a new one. Pressurized to 20 psi and the passenger footwell filled with coolant.

Im guessing the heater core was being held together with thoughts and prayers and it just couldn’t handle a good cleaning.


 

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Here’s a fun one.

So I did a heater core flush this week, using a technique I read here; use a submersible pump in a bucket of water with rad cleaner and let the pump run for a few days. Did it each way (in the top, out the bottom then in the bottom and out the top). I had full flow almost instantly. Then after 48 hours of flushing I blew some compressed air through just to be sure, no restrictions.

Didn’t get too much debris out, but when I put it all back together and bled I went for a drive and I had heat! Win, right?

No.

I came out a few hours later to do another bleed for good measure and there’s coolant under the Jeep. Thought it was one of the clamps on the heater hose on the firewall so I installed a new one. Pressurized to 20 psi and the passenger footwell filled with coolant.

Im guessing the heater core was being held together with thoughts and prayers and it just couldn’t handle a good cleaning.


I read about a procedure like that somewhere and considered it for a second while replacing my water pump then quickly decided against it for the reason you just described. It’s -34°c here and I need what little heat I have to get me through to spring when I can replace a ton of parts.


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cars have about 15 pounds pressure in rad. you may have 50 with a pump or garden hose so you blew it apart. gotta start slow,just trickle water thru both ways.
next time...
 

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Discussion Starter · #4 · (Edited)
cars have about 15 pounds pressure in rad. you may have 50 with a pump or garden hose so you blew it apart. gotta start slow,just trickle water thru both ways.
next time...
No.

Our systems are rated for 21 psi.

The garden hose was on a 1/4 hp submersible pump, not municipal water.

If the flush had “blown it apart” from the pressure of the pump it would have leaked the same if not more during the course of the treatment and emptied the bucket.

I think it’s more likely that some old headgaskets sealer was dissolved and allowed for a leak when the system went back under pressure.
 

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I think it’s more likely that some old headgaskets sealer was dissolved and allowed for a leak when the system went back under pressure.
+1.

This was destined to fail, pump or no pump. At least it failed in a controlled environment and not trekking the Yukon 1000's of miles from home. I'd like to hear how your core replacement goes - I haven't done one in a WJ (yet). It does not sound fun. If I did have to do it, I'd probably do the blend door fix while I was in there.
 

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Discussion Starter · #9 ·
+1.

This was destined to fail, pump or no pump. At least it failed in a controlled environment and not trekking the Yukon 1000's of miles from home. I'd like to hear how your core replacement goes - I haven't done one in a WJ (yet). It does not sound fun. If I did have to do it, I'd probably do the blend door fix while I was in there.
I’ve got the replacement core and some nice aluminum blend doors ready to go! I was just hoping for the cost of the rad cleaner and time that I could fix it this way before tearing the car apart.

Will report back.
 

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I’ve got the replacement core and some nice aluminum blend doors ready to go! I was just hoping for the cost of the rad cleaner and time that I could fix it this way before tearing the car apart.

Will report back.
Try a different rad seal.

I've used Bars Leaks or Bars Seal many many times.
I've never had a blocked rad.

 

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Here’s a fun one.

So I did a heater core flush this week, using a technique I read here; use a submersible pump in a bucket of water with rad cleaner and let the pump run for a few days. Did it each way (in the top, out the bottom then in the bottom and out the top). I had full flow almost instantly. Then after 48 hours of flushing I blew some compressed air through just to be sure, no restrictions.

Didn’t get too much debris out, but when I put it all back together and bled I went for a drive and I had heat! Win, right?

No.

I came out a few hours later to do another bleed for good measure and there’s coolant under the Jeep. Thought it was one of the clamps on the heater hose on the firewall so I installed a new one. Pressurized to 20 psi and the passenger footwell filled with coolant.

Im guessing the heater core was being held together with thoughts and prayers and it just couldn’t handle a good cleaning.
Sometimes good deeds get punished.
Personally, I would never pressure flush a cooling system on a 20 yo vehicle, unless it was a last resort, for the situation you ran into. I feel for ya.
You quoted the pressure at 20 psi which seems high. Most systems run at 15 psi IIRC, I quick google found this spec (16-18psi)
I tend to like the 2-step 'acid' flush. but no guarantee this would not have resulted in the same result that you saw.
+1 on the Bars stop leak.
Good luck
J
 

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Discussion Starter · #13 ·
Sometimes good deeds get punished.
Personally, I would never pressure flush a cooling system on a 20 yo vehicle, unless it was a last resort, for the situation you ran into. I feel for ya.
You quoted the pressure at 20 psi which seems high. Most systems run at 15 psi IIRC, I quick google found this spec (16-18psi)
I tend to like the 2-step 'acid' flush. but no guarantee this would not have resulted in the same result that you saw.
+1 on the Bars stop leak.
Good luck
J
My 01 4.7 uses rad caps between 18-20 psi, be it mopar, stant or gates etc. Granted that’s a maximum threshold and your right it typically operates around 15 psi.

Actually, stop leak is what diminished my heat a number of years ago when it blew a head gasket and I didn’t have time to fix it. I’d say I lost 60% of my heat output permanently because of it. I know other people have had issues as well. At any rate, that heater core lasted me 320,000 miles and got me through 20 Canadian winters, it was time, lol.

 

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Sometimes good deeds get punished.
Personally, I would never pressure flush a cooling system on a 20 yo vehicle, unless it was a last resort, for the situation you ran into. I feel for ya.
You quoted the pressure at 20 psi which seems high. Most systems run at 15 psi IIRC, I quick google found this spec (16-18psi)
I tend to like the 2-step 'acid' flush. but no guarantee this would not have resulted in the same result that you saw.
+1 on the Bars stop leak.
Good luck
J
Accordingly, the WJ's cap releases at 17psi, plus or minus whatever.
20PSI should be safe with a system that wasn't going to blow the next time the car was stuck in traffic on a really hot day.
Whilst inconvenient, this mishap could be blessing in disguise.
Although a cursed nuisance at any time.

1/4hp seems overkill, a small 12v submersible pump would have done the biz as a high flow rate isn't necessary.

However, as the system was open flow, ie there was no pressure cap / valve involved, the pressure involved would only have reached 20psi if the flow rate was exceedingly low.

I daresay the flow rate was as SJB expected, if not, well perhaps he was a bit of a silly billy letting it build pressure.

Perhaps in future it would be wiser to have 2 reservoirs and no pump.

The 2 reservoirs at about the same level to start.
Both reservoirs to be above heater radiator level.

Fill the lower reservoir with flush until the higher reservoir is just beginning to fill.
Leave the system for a while.
Raise one reservoir until the flush nearly fills the other.
And so on until you think the job is done / get bored.
 

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My sixpence says your rad cleaner dissolved the sealer that stopped an earlier leak.
Hence I suggested using a Bars sealer once you'd solved the flow problem.

Just as my compressor doesn't build pressure when the outlet is open, a garden hose and a pump won't build pressure unless the rad's outlet is closed.
 

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He was already planning to put metal blend doors in with a new heater core and evaporator anyway. It was super cold and he lost heat in the middle of winter. Was worth a try and that core was leaking for a long *** time.
 

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He was already planning to put metal blend doors in with a new heater core and evaporator anyway. It was super cold and he lost heat in the middle of winter. Was worth a try and that core was leaking for a long *** time.
What does the word "Poke" mean where you used it above please X?
 
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