P0128 Code

So, I obviously don't want you to burn your hand, but if you squeeze the upper hose slightly, you'll definitely feel the fluid thru the hose.
That being said, if you are feeling the fluid flowing from start-up, you have a t-stat stuck open. But your temps tell me otherwise.
Changing a t-stat is less than an hour and it's not expensive. The t-stat w/housing is about $38.
 
@Anybodyhome thank you for the info. My dad would always tell me that and I say “i just feel vibrations of the engine”, been 30 years and still have an issue.

Update, wife didn’t drive yesterday so didn’t have anything. She drove it to work this morning. Outside temp 58, 12 miles mostly surface streets, average speed I’d assume 45. The information panel showed the temp at 185 the vast majority of the time. She said it did bounce up to 192 but basically stayed at 185 most of the time. Yes heater on full blast.

For fun I rolled down my windows this morning, turned heater on full blast doing 65-70 on freeway. Temps were between 188-195. Once I rolled up the windows and turned down the heat they basically stayed at 200.

Thanks for the info on the t-stat. Yes should be simple, replaced few in my lifetime. Then again replaced, added coolant or flushed and went on my way (Been a while though). Seems like new cars and JK’s are picky on getting topped off, filled up correctly or trapping air in the system, mixing fluids if PO put in wrong one. I’d replace it all, just not sure if there is a trick to getting all the old out. Never really worried about it much before, was all same type of antifreeze.
 
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@Anybodyhome thank you for the info. My dad would always tell me that and I say “i just feel vibrations of the engine”, been 30 years and still have an issue.

Update, wife didn’t drive yesterday so didn’t have anything. She drove it to work this morning. Outside temp 58, 12 miles mostly surface streets, average speed I’d assume 45. The information panel showed the temp at 185 the vast majority of the time. She said it did bounce up to 192 but basically stayed at 185 most of the time. Yes heater on full blast.

For fun I rolled down my windows this morning, turned heater on full blast doing 65-70 on freeway. Temps were between 188-195. Once I rolled up the windows and turned down the heat they basically stayed at 200.

Thanks for the info on the t-stat. Yes should be simple, replaced few in my lifetime. Then again replaced, added coolant or flushed and went on my way (Been a while though). Seems like new cars and JK’s are picky on getting topped off, filled up correctly or trapping air in the system, mixing fluids if PO put in wrong one. I’d replace it all, just not sure if there is a trick to getting all the old out. Never really worried about it much before, was all same type of antifreeze.
When I took mine out for a spin after the t-stat install the temps shot up and bounced all over. Took it home, let it cool and popped the rad cap and began topping it off and getting the air out. No worries since.
 
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As a note to others following this conversation, if the coolant in the system is too low, it can not build enough pressure to pull from the overfill reservoir and needs to be filled directly into the radiator cap. Don't open the cap on a hot engine.
 
Update - You all may think I am crazy. But I tried my theory. I cleared the code. My wife drove two days with no heater on in the morning and the temp rose and stayed right at 200 and no CEL light has come. So it seems that when its in the high 50’s - low 60’s and she uses the heater full blast the entire trip to work in the morning the coolant temp basically reaches a high of 185 and which in turns causes the the CEL light to come saying the engine is operating below temp.

Other then this all seems normal, temps seem to be the normal operating range. Also this is only the case when the doors and freedom panels are off so obivisoly :)the cab never heats up . Which is why the heater is running full blast the entire time.
 
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Update - You all may think I am crazy. But I tried my theory. I cleared the code. My wife drove two days with no heater on in the morning and the temp rose and stayed right at 200 and no CEL light has come. So it seems that when its in the high 50’s - low 60’s and she uses the heater full blast the entire trip to work in the morning the coolant temp basically reaches a high of 185 and which in turns causes the the CEL light to come saying the engine is operating below temp.

Other then this all seems normal, temps seem to be the normal operating range. Also this is only the case when the doors and freedom panels are off so obivisoly :)the cab never heats up . Which is why the heater is running full blast the entire time.
Saw heater full blast and thought why? Then I remembered you are in CA and 50 is cold there. Lol. Glad you sorted it out.
 
@Largehit71 very funny! But true I suppose. I just can’t believe the settings are that sensitive. When I had my YJ i had a bikini top some sort of vinyl half doors and drove all over the place with the heater on well into October.
 
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