ZJ Cooling System has me baffled - JeepForum.com
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post #1 of 25 Old 12-04-2020, 07:18 PM Thread Starter
TonyStadnichuk
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ZJ Cooling System has me baffled

97 ZJ 5.2 Litre
Temperature on the guage was not coming up. Vehicle slow to warm up. I thought I had a 180F thermostat in there. Bought a 195F. Went to change it and the one in there was a 195F, about 2 years old. Put the new one in, no change in temp on the guage. Checked rad cap and it was a 13 psi. Bought a 16 psi and put it on (manual calls for an 18 psi but I don't trust those old heater hoses. Anyway, still not heating up to where it should be. Infrared readings on the hoses are as follows:
Top Rad Hose: 175F
Bottom Rad Hose: 152F
Heater Core In: 176F
Heater Core out: 168F
Could I have two thermostats bad in a row, or what am I missing?
Sorry pic twisted on me and I don't know how to flip it.

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post #2 of 25 Old 12-04-2020, 07:23 PM
PolkaPower
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Old hoses? Why not replace them and get a proper lb cap?

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post #3 of 25 Old 12-04-2020, 08:38 PM
jtec
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hoses, cap, perfect time Be brave do the by pass hose now.

My WAG - replace coolant sensor....
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post #4 of 25 Old 12-05-2020, 06:08 AM
HighLonesome
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16 lb cap will work fine. But yea a busted hose is a show stopper.
Isn't the temp in the pic where it should be?
No offense but the thermostat will fit upside down... lol
Where are you located? Wondering what the ambient temp is.
How much driving did you do before making the temp measurements?
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post #5 of 25 Old 12-05-2020, 07:38 AM
V8GCZJ
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Quote:
Where are you located? Wondering what the ambient temp is.
How much driving did you do before making the temp measurements?

Exact same thing i was wondering. Need to list details.
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post #6 of 25 Old 12-05-2020, 07:54 AM
HighLonesome
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Originally Posted by V8GCZJ View Post
Exact same thing i was wondering. Need to list details.
My initial thoughts are nothing is wrong? Or maybe the heater isn't working well.
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post #7 of 25 Old 12-05-2020, 11:00 AM Thread Starter
TonyStadnichuk
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Sorry. Ambient temp is just above freezing. 4C (Canada) Thermostat is definitely in there correctly. As you say, the 16 lb cap should be just fine. All infrared readings are taken after about an hour of driving. If there was an air lock, it should be overheating. I am going to remove the thermostat today and do the pot on the stove test. There is no need to change temp sensor as the gauge has been verified by infrared thermometer. A plugged rad would give me an overheat problem so that's not it. The gauge needle should be just under the "100" mark if it was hitting the proper temperature.
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post #8 of 25 Old 12-05-2020, 12:16 PM
Timo_90xj
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I see nothing wrong with your engine operating temperature, it's right where it's supposed to be.
I've got a 195F Stant t'stat, my engine temp has been rock-steady at ~95C for the past few years no matter if it's +25C or -25C. It was around 100C before replacing the original radiator and doing other cooling system upgrades.

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post #9 of 25 Old 12-05-2020, 04:48 PM Thread Starter
TonyStadnichuk
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You guys might be right! For some reason I always thought the guage was just under the 100 mark. So I picked up a new thermostat, did the in the pot on the stove test and the new one opened up at 198F. I took the thermostat out of the Jeep and did the same test. It also opened up around that 196F. So much for that. I put the old one back in and ran the engine for about half an hour with the rad cap off. It eventually did a big blurb and proceeded to boil over. I shut everything down, put the rad cap back on and headed for the car wash to get all the coolant off the engine and inner fenders. At that point it was running super hot. Opened the cap(carefully) and let off the steam and overflow. Topped up the coolant (it took pretty much a complete jug) Took it for another drive. The guage is a little higher and there is considerable heat coming through the vents. Maybe this is as good as it gets. I do have to do a flush come spring because it does overheat. This will get me through the winter.
On another note, I notice a lot of rads seem to get changed out on these ZJ's. I still have the original rad. What typically happens to them? Should I source another rad before I get a flush done?
And thanks everyone for your input!
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post #10 of 25 Old 12-05-2020, 05:07 PM
Rapidrob
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No, I would not. I've been dealing with trapped air for awhile. The engine head is a massive reservoir for coolant, it is like Carlsbad Caverns in size.
Park the Jeep on a steep sloped for several minutes and rev the engine to get the antifreeze flowing. It should remove most of the trapped air to the radiator where you can vent it to the overflow bottle by cracking the radiator cap.

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post #11 of 25 Old 12-05-2020, 05:23 PM
RedRiverT
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Tony, as you discovered, you had air trapped in the system. There is probably still some. Check the overflow tank after the next 5 or 6 times you drive it and keep it filled between the Min / Max lines. If you don't have a leak, it should purge itself. Of course, you may very well have a leak and that's why you had trapped air. You could have a steam leak high on the radiator and it doesn't drip, just slowly loses coolant vapor.

I know my rad, and I think it is a common failure, had one of the side tanks split open. I had started it and turned the AC on to eat lunch, then heard a pop after a few minutes.

The replacement from OReilly Auto Parts had a leak at the top seam, which was under the shroud, and that tormented me for months. I finally saw steam coming out of the grill one day after a thunderstorm when it was real humid and that led me to the leak. OReilly's gave me a warranty rad and it has worked properly for years now.
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post #12 of 25 Old 12-05-2020, 10:07 PM
riiz
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Quote:
Originally Posted by TonyStadnichuk View Post
On another note, I notice a lot of rads seem to get changed out on these ZJ's. I still have the original rad. What typically happens to them? Should I source another rad before I get a flush done?
And thanks everyone for your input!
The plastic tanks on the radiator usually spring a leak after 20+ years of heat and pressures cycles, they fail.
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post #13 of 25 Old 12-06-2020, 04:15 PM Thread Starter
TonyStadnichuk
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OK, last kick at the cat for the weekend. I checked the overflow and it was low. Warmed up the jeep and grabbed another jug of 50/50 coolant. Drove around for awhile, found a nice incline and backed down it. Revved up the engine for a couple minutes. Cracked the rad cap to the first notch (with gloves on and a couple rags over top) A little air may have escaped but mostly liquid..And it was HOT.
Came home and did another infrared temp measurement. Heater hose in is about 177. Out is about 165. Top rad hose is 188 and lower hose around 165. I am guessing that the thickness of the hoses must take 20 degrees from the actual measurement. I "shot" the metal housing above the thermostat and it read 193. I am thinking that is about as good as it gets. I may do a pressure test this week as that is something I have not done. Thanks everyone for your input!
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post #14 of 25 Old 12-06-2020, 04:55 PM
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You want to do a "nose-up" to purge the air through the T-stat and out of the head.

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post #15 of 25 Old 12-06-2020, 05:32 PM
freddy2times123
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Quote:
Originally Posted by Timo_90xj View Post
I see nothing wrong with your engine operating temperature, it's right where it's supposed to be.
I've got a 195F Stant t'stat, my engine temp has been rock-steady at ~95C for the past few years no matter if it's +25C or -25C. It was around 100C before replacing the original radiator and doing other cooling system upgrades.
hes right

i see no need for testing.
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