I just changed my thermostat housing after my 2012 base started doing the fan running all the time thing. I've had to replace 3 thermostat housings in my 5 years with this car, so as soon as the fan started running all the time, I just went straight for the thermostat housing, although it was not showing any codes. I put on a new aftermarket one and the only change was now I have a p0128 and p0597 codes. I took off the aftermarket and replaced with OEM, no change. I also put a new plug/pigtail that connects the temp/thermostat sensors to the main loom, thinking I could have a bad connection or broken wire. No change

Here's where I'm stumped. It doesn't seem that coolant is circulating. After filling it up, I've tried bleeding the system, but get no coolant out of the bleeder. Also, the top rad hose gets warm, but the bottom stays cold. And, there's no heat. So, that would lead me to believe that we have no circulation.

My current hypothesis is that A. There's air trapped in the system or B. that I have a clogged radiator. I will add that when I bought this car, I did a head gasket on it and it was full of head gasket repair goop. I cleaned all that junk out, but am wondering if it's managed to find it's way into the radiator and create a clog.

I'm in need of some guidance, anyone have any ideas. Thanks

 

2013 JCW here - I'm having a similar issue.

Bleeding the air out can be a bugger. If there's air trapped @ the temp sensor - the fan will run.

I also had a bad HVAC control head that forced the fan to run.

I currently think I have everything correct - but my coolant temp won't go over 150°F.

 

So I was able to finally resolve it, I did several things and I'm not sure which exactly did the trick, but I do think it was ultimately air in the system.
I changed the water pump, probably unneccesarily, I replaced the crossover pipe which I found a crack in and I jacked up the drivers side to get the expansion tank higher.

Then, I unplugged the fan, hooked up the OBD scanner to monitor temp and I ran it up to 105 degrees C. My theory is that the thermostat needed to open to help burp the system. I shut it off, let it cool down, cleared the code and fired it back up with no CEL. It's been good since.

Hope that helps