P0128 (I know its been talked about)

[Eric Suderman]

The KJ threw a P0128 yesterday, which from reading other forums could be IAT, ECT, or thermostat. I burped the system today but there didnt seem to be any air bubbles. My question is, if a scan tool reads fairly normal temps from both of those sensors then should I assume they both are still good and narrow it down to the tstat? I would like to know thats where my issue is before having to drain the coolant in the middle of November and Seattle rain. Or could one of those sensors be bad and still showing fairly normal temps? I'm pretty sure I filled a bit more coolant than water when i changed the heater core last month, could that cause an issue?

 

[LibertyTC]

Welcome to the forums.
HOAT or Zerex G-05 coolant only for our Jeeps. Has any other coolant types ever been added before?
Code 0128 is directly related to the thermostat.
Probably best to drain the system & install a new Mopar Thermostat.
Coolant temps can be read by scan tools, if stuck open, too long to warm up, it will set this code.
Further info can be found in Factory Service Manual. What year of KJ do you have?

 

[Eric Suderman]

When I changed the heater core the coolant that came out was green I also have noticed air sounds in the heater core so I'm probably gonna take it to a shop for a flush to solve both of those. Could air cause the p0128?

 

[LibertyTC]

Green coolant not good. Best flush is...Find a shop that has a pressurized coolant re-circulating machine. (dealers often have one)
Ensure that Hoat coolant or Zerex G-05 only is used.
Air is something that can be bled out at top rad hose hex.
Installing the Mopar thermostat should solve your issue as it has it's own air bleed also built into the thermostat.

 

[Eric Suderman]

I'll see about having my shop do the thermostat while they're at it, and make sure they use the mopar part. I'd do it all myself but it's 30-40 degrees out so dealing with coolant doesn't sound fun, especially if I may still end up having a shop bleed it anyway. I've used the bleeder but there wasn't any air there, seems to be mainly in the heater core (for now).

 

[LibertyTC]

With green coolant in core it's bad news. You want to remove everything and replace it.. & the only way to do it right is with a re-circulation machine.
The green coolant does not mix well with Hoat and it causes a gel like substance/coagulates and can cause water pump, broken plastic impellers.
Keep in mind in a proper mixture it includes distilled water, not good ever to flush with tap water.

 

[Eric Suderman]

Noted. From what I'm seeing on thermostats they're all made by motorad now? I found one on Amazon that says it's mopar but has some mixed reviews based on the motorad stamp being on the Stat itself, is this the part I want or should I keep looking?

 

[Eric Suderman]

I got a coolant flush and thermostat scheduled at my local shop, having them do transmission fluid and filter while they're at it for a total of $750... woof. I have parts ordered for a PCV update. Any other systems I should be particularly worried about on a mistreated kj?

 

[LibertyTC]

Make absolutely sure they use the Mopar thermostat part, which is # 68174083AA.
Have you serviced the DINO rear diff gear oil lately? What year is your Jeep ??