Hey all, I have a 2018 Charger with a 3.6L V-6. CEL came on with a code P0128 (Thermostat Rationality). Took it in to my mechanic for a new Thermostat and found that the Radiator had a small leak. So, my mechanic replaced the Radiator and Thermostat with OEM Mopar parts. Now the engine heats up fine, but when it gets to operating temperature, the temp gauge is erratic. Runs between 201* and 212*, well within range, but will jump up and down 4*-8* in a matter of a second or two. I replaced the Thermostat, and it still does the same thing. I thought it may have trapped air, but I've driven it for 2 weeks and it stays the same. Before the work was done, the car would heat to 185* ( a little low, but no CEL until a couple weeks ago ) and the temp gauge didn't vary one degree. Is this normal for a properly operating thermostat? Or do I possibly have another issue? Appreciate any advice. Thanks!!

 

Bad connection at the sensor? I suspect that is an electrical problem......

 

It sounds like you possibly still have air in the system, even after 2 weeks. Does the shop you trust have a cooling system vacuum fill system?

-Rod

 

OK, so I've checked the electrical connection at the coolant temp sensor, pin tested the terminals, checks OK. I am not sure if my shop has a vacuum fill system. BUT, when I was checking my coolant sensor connection, I did a scan around the engine and I noticed my oil cooler is leaking (oil at least). It's a Dorman all Aluminum unit (but the OEM Cooler, that's the way Dorman sold them back then) installed about 3 years ago wit Mopar OEM gaskets/seals. So the cooler itself may be leaking also? Tough to see coolant when there is oil in the engine valley. Thinking of replacing the whole unit with a Mishimoto cooler. Sound reasonable as a place to start? Any thoughts are appreciated!!

 

Oil finding it's way into the cooling system is, unfortunately, not an unheard of problem. I chalk it up to a poor design..... So, replacing it completely is very likely the best plan.