Thermostat P0128

[Snagster123]

Just got a P0128 CEL code.... engine appears to be running about 185deg which is a little low. Interestingly... the water pump was recently replaced back in August 2025 and now the thermostat is having an issue??? Seems a bit coincidental. Going back in the shop this Friday.

 

[RamCares]

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[dieselscout80]

I had that error on my 2020 see the below link for details.

It’s not a bad job. The only tricky part is the releasing the electrical connector on the thermostat.

D

Thread '6.4 HEMI Thermostat R&R 2020 Ram 2500'

Apr 18, 2025

My thermostat was setting off a service engine code for an irrational thermostat, so I swapped it out.

The radiator drain is a yellow wing nut and 5/16” hose fits on the drain. I drained just less than 2 gallons from the radiator and it kept me from spilling much when the thermostat was removed.

I undid my air filter box lid and held it up with a tarp strap.

There are two bolts (13mm socket) and I used a couple long extension the one with the socket was a wobble extension. I left the hose attached to pull the thermostat off. There is a marked link on hose that lines up with the tab on...

• dieselscout80
• Replies: 17
• Forum: 6.4 Hemi V8

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