1. OEM part numbers were for a housing with thermostat together as one assembly.
2. Plastic is prone to failing over time.
3. Because most people can't remove the thermostat from the plastic housing without destroying one or the other.

 

Thanks ratchet


I went to dealer to get the hoat antifreeze last week because my reservoir was down to add line (6 years old) and also heard that maybe that could throw the 128 code ??
I'm talking to parts guy and , although he couldn't confirm ( sealed in bag/ and I was not buying it yet) ) , the therm. he thought, has to be sitting at a certain position in housing to work properly and may also be difficult to separate from housing.
I would assume the therm has to lock into housing properly but to say it has to sit in exact same position as before or it wont work properly seemed like a stretch but, I don't know.
Anyway, a few hundred miles and a week later, topping off the reservoir did not make the engine light go off so I guess i'll have to go buy the whole housing ( 40.00)
After topping off reservoir I see that it leaked a little onto floor ( but still to the full mark on reservoir) on same side as reservoir but see no wetness at lower hose and, radiator looks dry every wear.
Dealer was saying beside a lot of faulty thermostats, that the seam of the radiators is another problem but mine looks dry.
It only came from somewhere after topping reservoir off .
Radiator is full so I guess the slight leak does not matter

 

I replaced my thermostat on my 2011 3.6. The aftermarket thermostat came in a fixed position in the housing. It was about $35.00 on Amazon.

When you do the job be sure to clean the mating surface thoroughly. The gasket is actually a thick o-ring.

 

I purchased a new thermostat last year (20,000 miles ago) and replaced it without replacing the housing. It was easier than on an old Jeep because the non-paper gasket. No reason to replace the housing unless it is cracked.

 

I just did mine at 116K. Purchase the whole thermostat assembly. Its not that much and only buy OEM. As one poster already noted, the plastic may crack, especially when reinstalling. The last thing you want is an antifreeze leak after just replacing it. The $$ savings by just replacing the thermostat is not worth the potential problem.