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Discussion Starter · #1 ·
Hello this is my second post on the forum (I’ve gotten a little lost lol) and it’s with a problem that I’ve been fighting for a few days now.
Jeep: 2006 tj 2.4L I4

Alright, initially the Jeep got a check engine light (P0128) but there didn’t seem to be any spike in engine temp or loss but something had to trigger it. Figured ok I’ll replace the thermostat and coolant sensor.
Got a new sensor and a motorad thermostat. Drained, flushed, and put in the new parts. Bled the radiator but I couldn’t get up to my previous normal temperature which had been 200~ degrees Fahrenheit, and instead was sitting 170~. Thought ok maybe the thermostat came bad and is stuck open or the gasket on it had seemed a little weird and maybe coolant is getting through. Even checked the temp with an obd scanner and was matching my temperature gauge. Then I drained the coolant out, got the thermostat and it was fine, although the gasket was a little gnarled up.
With this in mind I wasn’t sure why I wasn’t getting up to normal temp as I do have limited knowledge and this work is new to me.
Went ahead and got a mopar thermostat because oem should be a straight shot. Got the thermostat, drained the coolant, put it in, and proceeded to bleed the radiator. And was hanging out at 196 degrees no problem.
Imagine my surprise when I woke up this morning and the Jeep couldn’t get above 174 degrees. I’m honestly at a loss here and am not sure where the mistake I made or thing I didn’t check is at.
When turned on later the engine did idle at around 203, but when driving would go back down to 170~ degrees. As I write this I attempted to bleed the radiator again because why not but couldn’t get the engine to idle above 176.
Of course I am eager for anyone’s insight as to the solving of my problem and would greatly appreciate it, thank you for your time and possible fixes!
 

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Real Jeeps have dents
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29,304 Posts
I never buy el-cheapo sensors from my Jeeps, and only buy Stant or Mopar thermostats. A faulty thermostat is always a possibility. You may have lucked out and got two in a row.

The cooling system is self bleeding, after several short trips or warm up and cool down cycles, all the air should have worked its way out. This self bleeding, and proper temperature regulation depends on a correctly functioning radiator cap.

I would buy a new radiator cap.

Follow the OBD-II self-diagnostics for troubleshooting.

P0128 JEEP code possible causes
  • Leaking or stuck open thermostat
  • Low engine coolant level
  • Insufficient warm up time
  • Faulty engine coolant temperature sensor
  • Engine coolant temperature sensor wire harness is open or shorted
  • Engine coolant temperature sensor circuit poor electrical connections (Looked for corroded, bent, or pushed back wire plug pins.)
 

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Got a new sensor and a motorad thermostat.
Was it one of their fail-safe models? Those are known to fail in the open position way too easily. Stick with better brand thermostats like Stant, like their SuperStat, or a Mopar. Make sure it has the required 195 degree rating too.
 

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Discussion Starter · #5 ·
Fan’s off, only comes on if the defroster’s on.ook me far too long to learn how to reply.
 

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Discussion Starter · #6 ·
Got a new sensor and a motorad thermostat.
Was it one of their fail-safe models? Those are known to fail in the open position way too easily. Stick with better brand thermostats like Stant, like their SuperStat, or a Mopar. Make sure it has the required 195 degree rating too.
Put a mopar thermostat in there and now while driving I get around 174 degrees. Idle in the garage It gets above 196. Does this indicate anything?
 

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Put a mopar thermostat in there and now while driving I get around 174 degrees. Idle in the garage It gets above 196. Does this indicate anything?
That indicates it's either stuck open, it's not seated correctly, or it doesn't have the correct 195 degree rating. 165 and 180 degree thermostats are incorrect for the Wrangler TJ.
 
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