6.4 HEMI Thermostat R&R 2020 Ram 2500

[dieselscout80]

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 the thermostat.

I topped off the overflow tank and burped it by squeezing the lower radiator hose.

It is not a bad job but the electrical connector on it is not easy to disconnect and reconnect.

 

[dieselscout80]

If anyone knows how that electrical connector is supposed to work let me know

 

[whitexc]

I can’t help much but I’m intrigued by this “irrational thermostat” message. Did it set a light? Symptoms?


Sent from me

 

[Jimmy07]

If anyone knows how that electrical connector is supposed to work let me know

Pull the release lever (that you push down on with your thumb) back one click. Then it will be unlocked so you can press down on the lever to release the connector.

 

[jsalbre]

I've got no useful comments on the thermostat, but I'm definitely stealing your tarp strap trick for the air filter box lid. I don't know why I never thought of something like that. It's always such a fight with that thing that I usually end up pulling it off at the hose.

 

[dieselscout80]

Pull the release lever (that you push down on with your thumb) back one click. Then it will be unlocked so you can press down on the lever to release the connector.

Thanks @Jimmy07

Is that release lever available for purchase or is the whole connector available?

 

[Jimmy07]

Thanks @Jimmy07

Is that release lever available for purchase or is the whole connector available?

TE Connectivity 1-1924067-1 is the whole connector.

 

[dieselscout80]

I pulled this load today after the thermostat swap with no issues.

The first pic is on a hill and it stayed in 8th most of the way up it. You got to love 4.10 gears. However, I could be convinced that 4.30/4.44 gears are better.

 

[dieselscout80]

I cleared the P0128 code with JScan however the permanent code did not clear until it went through about 3 drive cycles. It did go away though.

 

[dieselscout80]

I can’t help much but I’m intrigued by this “irrational thermostat” message. Did it set a light? Symptoms?


Sent from me

Yes the code was P0128 and the service engine light did come on.

 

[whitexc]

I cleared the P0128 code with JScan however the permanent did not clear until it went through about 3 drive cycles. It did go away though.

No joke….it had an issue working rationally. Thanks for posting this stuff. Some of our trucks are aging and more of us will be dealing with repairs/fixes.


Sent from me

 

[dieselscout80]

It looks like the 6.4 thermostat electrical connector is to an actuator not a sensor. I cut the old one apart so I could see what the connector was doing.

I wonder what will happen if I put 12 volts to it?

 

[HD Rider]

Is there a coolant system bleed valve on the 6.4L hemi? What is the procedure to ensure the air gets out of the system after dumping the 2 gallons of coolant?
Nice pics and write-up on how to replace the thermostat. Thank you!

 

[dieselscout80]

Is there a coolant system bleed valve on the 6.4L hemi? What is the procedure to ensure the air gets out of the system after dumping the 2 gallons of coolant?
Nice pics and write-up on how to replace the thermostat. Thank you!

No bleeder is in the system, but I wish there was one.

The coolant reservoir and fill point is the highest point in the system so it self bleeds.

One word of caution I drained just less than 2 gallons. You need to add coolant slowly even after it starts going down. When mine burped I lost some coolant and ended up having to buy a third gallon.

I topped it off several times to get it to the maximum fill line.

It might be worth it to separate the upper radiator hose (it’s two pieces) and add coolant that way before starting the engine.

 

[dieselscout80]

The electrical part of the thermostat is a heater and gets hot when I put volts to it. It has about 15 ohms of resistance see attached pictures.

I could only remove the heater by cutting the metal/aluminum from around it.

I wonder what the purpose of the heater is? Could it cause the heater to open sooner to keep the heat under control?

 

[dieselscout80]

If one could remove the electrical part (heater) the thermostat portion can be removed.

 

[el_barto]

Nice work.

I had my thermostat stuck open a few years ago (2022). It was during winter, truck was not getting up to temperature. Had the same P0128 “irrational thermostat” error.
They replaced the t stat under warranty.

Interesting that the 6.4 doesn’t have a bleeder screw. My 2018 Grand Cherokee Pentastar V6 doesn’t either, made it a bit of a pain in the ass to bleed the coolant after replacing the water pump. I ended up borrowing my friends vacuum bleeder. Which works well once you figure out how to use it, and provided you have a powerful enough compressed air source…not great for road side repairs. Also it’s a pretty expensive tool.

 

[jabartram]

My OEM thermostat failed 3 years in. replaced it without draining the radiator, catch pan got about a gallon, installed a dorman, i just replaced the thermostat again today a year later.