ZJ Cooling System has me baffled - Page 2 - JeepForum.com
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post #16 of 25 Old 12-07-2020, 08:44 PM Thread Starter
TonyStadnichuk
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1997 ZJ 
 
Join Date: Jun 2019
Posts: 35
Yes, i did have the nose up. For now I think I am done. Will watch the overflow level for the next couple of drives and let everyone know. Thanks again for all the help!

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post #17 of 25 Old 12-08-2020, 10:16 PM
jpcallan
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1996 ZJ 
 
Join Date: Oct 2013
Location: Portland
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Thermostat Vent Hole

I don't have the V8, but on a 4.0L... When you replaced the thermostat, did you drill a 3/32" or so vent hole in the flange around the thermostat to match the Mopar factory supplied thermostat and install it as described in the factory service manual? See:

https://www.jeepforum.com/forum/f13/...79/index2.html

If you didn't drill an air vent hole and position it at 12 o'clock (I have yet to see any aftermarket thermostat supplied with the vent hole), you will have a temp problem because of air trapped in the top of the water jacket. Without the air vent hole the air can't escape until the tstat opens, and the tstat won't open because it's in an air bubble. These big air bubbles can even cause warped / cracked heads when the head gets really hot because air displaces the coolant, then the thermostat opens and relatively chilly coolant hits the hot cast iron.


Air entry via the heater core
--------------------------------

While several members mention pinhole openings in the radiator, another place I can tell you air gets into the cooling system is from pinholes in the heater core (horrible job to change out). The heater core seems to leak little coolant and very slowly, but when the system cools down and goes into a vacuum, it seems to readily admit air into the core. We found this out after years of the annoying "waterfall" or "babbling brook" noise coming from the passenger side dash. Failed Jeep copper/brass heater cores I've seen in person and online all appear to leak at a failed solder joint.

Last edited by jpcallan; 12-08-2020 at 10:21 PM. Reason: Clarify engine model
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post #18 of 25 Old 12-09-2020, 03:39 AM
i-joshua
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Location: La Coruna, Spain
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Quote:
Originally Posted by jpcallan View Post
I don't have the V8, but on a 4.0L... When you replaced the thermostat, did you drill a 3/32" or so vent hole in the flange around the thermostat to match the Mopar factory supplied thermostat and install it as described in the factory service manual? See:

https://www.jeepforum.com/forum/f13/...79/index2.html

If you didn't drill an air vent hole and position it at 12 o'clock (I have yet to see any aftermarket thermostat supplied with the vent hole), you will have a temp problem because of air trapped in the top of the water jacket. Without the air vent hole the air can't escape until the tstat opens, and the tstat won't open because it's in an air bubble. These big air bubbles can even cause warped / cracked heads when the head gets really hot because air displaces the coolant, then the thermostat opens and relatively chilly coolant hits the hot cast iron.


Air entry via the heater core
--------------------------------

While several members mention pinhole openings in the radiator, another place I can tell you air gets into the cooling system is from pinholes in the heater core (horrible job to change out). The heater core seems to leak little coolant and very slowly, but when the system cools down and goes into a vacuum, it seems to readily admit air into the core. We found this out after years of the annoying "waterfall" or "babbling brook" noise coming from the passenger side dash. Failed Jeep copper/brass heater cores I've seen in person and online all appear to leak at a failed solder joint.

This is very interesting. I would like to know if the hole in the thermostat would work on a 5.2 V8

ZJ 5.2 V8 from La Coruña, Spain
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post #19 of 25 Old 12-09-2020, 05:53 AM
Zilliver
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1998 ZJ 
 
Join Date: Sep 2015
Location: Vantaa <-> Tallinn
Posts: 717
You dont need that hole in the V8.

98 Grand Cherokee 5.9 - sold
95 Grand Cherokee 5.2 - sold
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post #20 of 25 Old 12-09-2020, 06:32 AM
HighLonesome
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Quote:
Originally Posted by Zilliver View Post
You dont need that hole in the V8.
I tried it on my V8 anyway. What I ended up with is a Jeep that took forever to warm up, especially in the winter of course. Not good because you want to go to closed loop mode quickly and stay there.
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post #21 of 25 Old 12-09-2020, 12:13 PM
LouC
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I put in a new OE stat in our '98 ZJ after about 20 years and didn't have to drill any holes for it to bleed, I used this Lisle funnel which works like a charm. Easy, no mess no hot running etc.
The temp you show looks fine. You can always hook up an OBD-II scanner and get the exact temp if curious.
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ZJ new thermostat.jpg   Lisle funnel.jpg  

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post #22 of 25 Old 12-13-2020, 03:19 PM Thread Starter
TonyStadnichuk
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1997 ZJ 
 
Join Date: Jun 2019
Posts: 35
Thanks again everyone. The babbling brook sound from the heater core is something I have heard on this Jeep for 14 years. Just thought it was the nature of the beast. I sure hope I don't have to change out a heater core. I looked at my Haynes manual and it is not pretty! If there were pinholes in the heater core, wouldn't at least some coolant end up on the passenger floor? I never thought of plugging my OBD2 into it. Will do that next round. Originally I got on this kick because the Jeep was taking so long to warm up. I guess I am used to the newer vehicles that start throwing heat within 5 minutes. When she gets warm, it is warm. Just slower than I would like. So now, the serpentine belt. Obviously I got coolant on the belt. Now it is chirping like a mad bird! The belt is perfect with no cracks. Has anyone ever had this problem and what did they do? I know I can just change out the belt but they are pricy and I hate replacing stuff that isn't wore out.
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post #23 of 25 Old 12-13-2020, 03:53 PM
Rapidrob
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Just wash the belt off with warm water. If still "chirping"adjust the tensioner.

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post #24 of 25 Old 12-14-2020, 09:07 AM
jeepjeepster
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LouC, Im pretty sure there is a bleed screw that you need to remove on the 5.7. I know you said the funnel worked well, but just a heads up if you or anyone else has any issues.

I know the funnel will not work on the 3.7/4.7 without removing the bleed screw.. Just tried it this past weekend and the funnel had quit bubbling, I had squeezed the upper hose many times, the heat still wasnt putting out heat, and the upper hose felt empty. I was struggling to get the bleed screw out having just removed it a month or so ago, so I was trying to warm up the engine so it would come out... I could feel the allen bit twisting so I was a bit worried, but it eventually came out and it took at least 1/3 gallon more coolant. I tried loosening the upper hose to let some air out but for whatever reason that didnt work too well.

1994 ZJ-I6 w/270,000 mi
1998 ZJ 5.9 w/66,000 mi Slate Black
2004 KJ w/108,000 mi
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post #25 of 25 Old 12-14-2020, 04:41 PM Thread Starter
TonyStadnichuk
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1997 ZJ 
 
Join Date: Jun 2019
Posts: 35
Warms soapy water? I can't do much with the tensioner. It is spring loaded. Not the end of the world if it chirps a bit. Can't hear it inside the cab! Thanks.
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