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Discussion Starter · #1 ·
I'm frustrated, help if you can. The first time this code when off I changed my Thermostat with a O' Riley's stat that did made my car sound like crap and idle strangely, then immediately changed it out with a Napa one. Shortly thereafter a code for the sensor went off so I changed it with one that I bought from Napa..... no codes for the past 400 miles but then BAM my check engine light went off again for the Thermostat.

The car never overheats and the guage reads at 210 on the dot when it's warmed up.

Please help if you can with any suggestions.
 

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Is air trapped in the cooling system??? If so, it needs to be burped out. And you're installing 195 degree NON-failsafe thermostats right?
 

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You could still have trapped air in the system. I would replace that failsafe thermostat asap, they have earned a terrible reputation for failing prematurely and too easily in the open position. Try to find a thermostat with an air bleed vent opening on the flange. Mount the thermostat with the vent hole at the top so any trapped air can easily escape.
 

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X 2 Jerry plus burp it with the front end up either jacked up or parked on a steep hill if you lack jack stands or ramps or free stuff from Craigslist to flex on.
 

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If the tstat is good, could it be a bad coolant temp sensor or bad connection at the sensor. I'm not sure about the TJs but I know many computerized GM motors have 2 coolant temp sensors. One is at or near the tstat for the ECM and the other is in the cylinder head for the gauge.
 

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Discussion Starter · #9 ·
The code is p0128 after looking it up it says thermostat rationality.

I changed the temp sensor a about a months ago. Ill have to research to see if there's 2 sensors? I checked the wiring and everything looked good grime what I could tell....
 

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The code is p0128 after looking it up it says thermostat rationality. I changed the temp sensor a about a months ago. Ill have to research to see if there's 2 sensors? I checked the wiring and everything looked good grime what I could tell....
I could be wrong, but I though there were two sensors. One for the gauge on the dash, and a different one that feeds the ECU.
 

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Also, have been guilty of forgetting to reconnect the sensor plug when changing the tstat (or tensioning the belt on my son's 97) and get a CEL right away, but it's always been when the Jeeps were cold so I don't know if it affected the gauge or not.
 

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Think we have one. Almost positive but Am not. You can down load a free fsm from jeepslimited
.com you have to register. It's legit no junk mail.
 

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You could still have trapped air in the system. I would replace that failsafe thermostat asap, they have earned a terrible reputation for failing prematurely and too easily in the open position. Try to find a thermostat with an air bleed vent opening on the flange. Mount the thermostat with the vent hole at the top so any trapped air can easily escape.
And if you can't find one with the air bleed (some have a "jiggle valve"), you can drill an 1/8" hole there and install with the hole up. The hole makes filling the system without an air bubble much easier.
 

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Nevermind...I was mistaken, looks like there's a sensor and a sending unit. If the gauge doesn't work sometimes it's the sending unit, not the sensor. But if the gauge is working, the sensor must be working.
 

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Well here is a newb question. I just got the code after I started the Jeep and took off without being warm up. So the engine light pop immediately. Anyway the code is P0128 for Thermostat.

So 2 questions:

1. What is meant by "I burped the radiator"? Is that with coolant without the cap or with coolant without the cap

2. What type of Thermostat is recommended for a TJ 2005 6cyl? I see some people say "Non-Failsafe 195ºF" or "thermostat with an air bleed vent opening on the flange"

Thanks
 

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Burping the radiator simply means getting any trapped air out. Can be done in many ways, Google will find a ton of articles on how to do it. In theory, our TJ's cooling system is self-burping.

Yes for sure you want a non-failsafe 195 degree thermostat. Some thermostats are marked "Failsafe" and you want to avoid that type since they commonly fail prematurely. The failsafe description doesn't mean it won't fail, it just means when they fail they'll fail in the open position. which causes them to lock in the open position which will cause the engine to take much longer to warm up, or not warm up at all if the ambient temperature conditions are cold.

Thermostats like the SuperStat by Stant have a bleed port inside that isn't visible. A SuperStat would be a good choice.

Some other thermostats have a bleed port punched into the flange as below in the first photo, and those with nothing for bleeding can simply have a bleed port drilled like in the second photo.
 

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Burping the radiator simply means getting any trapped air out. Can be done in many ways, Google will find a ton of articles on how to do it. In theory, our TJ's cooling system is self-burping.

Yes for sure you want a non-failsafe 195 degree thermostat. Some thermostats are marked "Failsafe" and you want to avoid that type since they commonly fail prematurely. The failsafe description doesn't mean it won't fail, it just means when they fail they'll fail in the open position. which causes them to lock in the open position which will cause the engine to take much longer to warm up, or not warm up at all if the ambient temperature conditions are cold.

Thermostats like the SuperStat by Stant have a bleed port inside that isn't visible. A SuperStat would be a good choice.

Some other thermostats have a bleed port punched into the flange as below in the first photo, and those with nothing for bleeding can simply have a bleed port drilled like in the second photo.

Thanks so much for the explanation!!!
 

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Burping the radiator simply means getting any trapped air out. Can be done in many ways, Google will find a ton of articles on how to do it. In theory, our TJ's cooling system is self-burping.

Yes for sure you want a non-failsafe 195 degree thermostat. Some thermostats are marked "Failsafe" and you want to avoid that type since they commonly fail prematurely. The failsafe description doesn't mean it won't fail, it just means when they fail they'll fail in the open position. which causes them to lock in the open position which will cause the engine to take much longer to warm up, or not warm up at all if the ambient temperature conditions are cold.

Thermostats like the SuperStat by Stant have a bleed port inside that isn't visible. A SuperStat would be a good choice.

Some other thermostats have a bleed port punched into the flange as below in the first photo, and those with nothing for bleeding can simply have a bleed port drilled like in the second photo.
I bought today a SuperStat by Stant 195 degres from Ad Auto but doesn't have the bleed port. I guess I will drill the hole if is necessary...????
:confused:
 

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I bought today a SuperStat by Stant 195 degres from Ad Auto but doesn't have the bleed port. I guess I will drill the hole if is necessary...????
:confused:
Remove the heater hose from the thermostat housing while adding coolant. That gives trapped air a very sufficient escape route.
 
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