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Unread 07-08-2009, 11:50 PM   #1
Bunkman007
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1998 zj 5.2 coolant won't circulate

Hello! I am in desperate need of any advice. I have a 1998 5.2 with the strangest problem I have ever encountered on a vehicle that I can't solve on my own. I'm beating my head against a wall daily! I take great care of my Jeep and as corny as it sounds its my baby. The engine has 154k, and it runs as good as when I got it at 70K. This ZJ has always run temp wise around 197-200deg on a 75deg day. Recently I noticed that it started reaching 210-220deg. Coolant ph was checked and is good. Then I felt the upper radiator hose when Jeep reached normal operating temp and the upper hose was limp indicating no coolant circulation. So I replaced the thermostat but the same problem still existed. Then I said what the hell the oem waterpump must be bad so I replaced it. Problem is still here. Tried another 195 thermo and then finally a dealership thermo plus new upper and lower radiator hoses, but I still have the same problem. Last thing I did was install a new coolant temp sensor thinking the gauge was inaccurate. STILL the coolant will only circulate when the Jeep reaches around 220-230deg. The worst part is without my kickass Flexilite blackmagic fan(thats doing all the work) my Jeep would overheat. This seems like an anomoly! Anyone seen this problem before? An advice on what next?

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Unread 07-09-2009, 08:32 AM   #2
EMTimZJ
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If you have a new T-stat, water pump, and temp sensor, and coolant DOES eventually flow, it sounds like your dash gauge is what is faulty.
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Unread 07-10-2009, 06:24 PM   #3
Bunkman007
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Hey! Thank you for the reply. I thought the gauge might be bad too, but I replaced the coolant temperature sensor which I thought controlled the gauge. The sensor that I replaced is next to the thermostat housing behind the alternator. I have a Chiltons manuel and the it is kind of confusing. It mentions a temp switch(for open loop/cold loop during warmup), and another sensor on the left side of the engine block below the exhaust manifold, but I intensively checked both sides of the block, and it doesn't exist. Must be a different model Jeep maybe. Is there something that I am missing? Another sensor to replace?
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Unread 07-10-2009, 06:31 PM   #4
Haleyrz
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is the connections between the sensor and gauge good? And this is a long shot as I'm not sure if there are fuses or relays that are linked to the cooling system, but if so, check those.
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Unread 07-11-2009, 03:13 AM   #5
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If the hose is soft then it does have a problem somewhere. Have you put a new cap on yet?
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Unread 07-11-2009, 07:06 AM   #6
newfieZJ
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do you eventually get LOTS of heat in the dash , I'm thinking blockage in the heater core or poor circulation in the rad
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Unread 07-12-2009, 03:25 PM   #7
Bunkman007
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Well for starters I want to thank everyone especially the 5.9 guy(radiator cap) for their advice. I solved the problem and I was quite suprised after all this, and the headache I caused for myself. The reason the coolant wouldn't flow after a new water pump and 3 thermostats was a bad radiator cap! I kinda feel like an idiot wrapped in a moron because this should of been the first thing I checked, but I didn't understanding how critical the cap is to completing the system. I thought how could a simple cap be the issue when it didn't indicate anything. I got a pressure tester and the system held perfect for ten minutes at 16lbs. The cap looked fine but only held 8lbs and it is suppose to hold 18 for the 5.2. For most people I described the problem to 9 out of 10 said bad waterpump or bad thermostat/stuck. O well I hope this helps someone else down the road. Now its time to replace the dam leaky rear main seal! Woooo hooooo! Peace to all. Seth
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Unread 07-12-2009, 08:57 PM   #8
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Your welcome.
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