P0128 Code After Coolant Overhaul

[Sgt Jarhead]

Another P0128 thread for you folks.

I did a coolant overhaul for my 06’ 4.0. Swapping the radiator, hoses, thermostat, water pump, fan clutch, down to the Thermostat Sensor using oem/equivalent products.

My current temp stays at 195* maybe a little less. Prior to the overhaul tempts were at 210 maybe a little higher at times. I doubled checked my thermostat (thinking it was faulty and replaced with mopar 195*) that was tested prior to installing. I’ve replaced the temp sensor (also mopar) and fan clutch (Hayden replacement stayed engaged).

With the new replacement fan it still looks like it stays engaged when cold, after running it a few minutes and of course after it’s fullly warmed up. There’s no difference in resistance. I’m not sure if I’m lucky enough to have 2 faulty fan clutches or maybe it’s as simple as burping the system more. (Thermostat does have a 1/8 hole to help burp it).

I’ll be attempting to burp the system again when I have a chance and thought I’d make a post to have another perspective given my current situation.

 

[Sgt Jarhead]

I put the Jeep on an incline and burped the system again and managed to get a few bubbles by the time it warmed up (at 195* again). Though I was messing with the upper heater hose that spilt a bit of fluid prior to burping the system. Currently letting it cool down to see if anything changes when I drive it later today.

Also, before I left my home I took a look under the hood while it was cooling down and noted light steam coming from under the top of the fan shroud. It’s likely just coolant that had overflowed from the top of the rad onto the fins though I thought I’d annotate this.

 

[Dawadog]

I’m getting the same code after doing the same thing to my 06 tj 4.0
Although I did not change the temp sensor. Mine only seems to pop up if it’s cold and I turn the heater blower fan on before it warms up. I have not noted the temp yet.

I was thinking possible air trapped.

im following for updates

 

[RMETeeJay]

Why did you replace the ECT sensor? Reinstall and then tell us what it reports for temps.

If the same, then it is likely the stat. Tell us what stat part number(s) you've tried.

 

[Sgt Jarhead]

The Code returned and I left it alone for a little bit.

Last weekend I noticed I was leaking coolant from the front of the oil pan where typically would be a sign of a bad water pump although mine was a new Mopar replacement. I popped the hood taking a good look around and noticed the hardline that connects to the top of the water pump that runs to the heater core was loose and slowly leaking at the threads.

Ended up pulling the pump, replacing the gasket and added thread sealant/tighten down the hardline to the water pump an extra turn. Nearly a week later no code so far . Temps now fall between 194-198* checking the data on my scanner. Which is still well under normal operating temps of 210* prior to the cooling overhaul. Not sure if maybe the colder weather in Southern Oregon compared to where the rig has lived most it’s life in Hawaii is a factor. As long as there’s no code I don’t really care at this point

 

[Sgt Jarhead]

Why did you replace the ECT sensor? Reinstall and then tell us what it reports for temps.

If the same, then it is likely the stat. Tell us what stat part number(s) you've tried.

I was out of ideas at that point and the only thing that hasn’t been replaced that’s part of the cooling system was the Thermostat Sensor. So I basically threw $ at it hoping it would solve the issue.

 

[Sgt Jarhead]

Well months later the code has not returned. Safe to say it’s finally been fixed. I imagine it had to do with the hardline on the water pump mentioned previously that attached to the hose for the heater core slowly leaking coolant. Likely helped that I burped the system some more after the fact.

 

[RobertJ]

Thanks for following up!

 

[Fortzen1305]

Did you do a full flush of the block and the heater core before you did the overhaul? I'm asking because I'm doing the overhaul soon on my 05 LJ and haven't done any cooling system work in the past. I've done every mod to my jeep myself but this one has me a bit intimidated.

 

[Chris]

Thanks for the follow-up indeed!

 

[Sgt Jarhead]

Did you do a full flush of the block and the heater core before you did the overhaul? I'm asking because I'm doing the overhaul soon on my 05 LJ and haven't done any cooling system work in the past. I've done every mod to my jeep myself but this one has me a bit intimidated.

Yes I did. I followed this as it carries all the correct part numbers/links to items not to mention hyper links for how to instructions where I found the idea of drilling 1/8 hole to my thermostat to burp the system easier.

It was my first time doing the cooling system and overall it was straight forward other than the hiccup I made by not tightening down the hard line that attaches to the water pump that connects to a soft line towards the heater core. The threads on the hardline attaching to the waterpump ended up leaking very slowly. Also I believe I may have not burped the system enough initially. I do believe the hole I drilled on my thermostat helped get the last bit of trapped air out over time/drive cycles because not long after my cooling temps read either dead center at 210 or just barely below.