RSOLVED-Thermostat stuck?
 

Help a fellow out and confirm my diagnose before I start panicking! Just had some major preventative work done on my X (latter part of June '14, see my thread "preventative time" for a pdf of what was replaced.) Has worked great since, but this evening on the way home from town, I get "coolant temp" message. Bring up Ktemp in the cluster, at 117! Pulled over immediately, turned off the engine, and within 5 minutes, I was down at 100. Turned heat and stratified all the way up, drove home, keeping an eye on Ktemp. Went up to 110 and sat there, would go up if I turned down the heat. Back down if the heat's on. The upper radiator hose is very hot, lower is cold. Heat still blowing hot. No coolant leaks under the X or under the hood, no green in the oil. Level in expansion tank is where it should be. Is my thermostat stuck? Dissapointed if it is, already, after my maintenance, but relieved as well if it's only that. Thot maybe my Indy didn't use an OE thermostat? Will be calling and asking. Have another thermostat ordered, also have a coolant temperature sensor laying in the shop that I haven't installed yet, that will be going in with the new thermostat. Opinions?

Edit: Just checked my pdf, that better have been an OE thermostat for $120!

2nd edit: Idled for 10 minutes with stratified on hot, heat on 90 with fan wide open. Won't go above 103. Turn everything off and to cold, sky high!

Sounds like stuck thermostat. Lower hose should be much "cooler" than the upper hose but it shouldn't be "cold" if there is a good flow of coolant passing through. Your radiator should also be hot if working correctly.

A scan of the car may confirm if the thermostat is stucked.

Might be the dual temp sensor going South. Happened to me, and it wasn't obvious to find the culprit. here's the thread with some insights.
I don't think the T-stat went bad that quick. To confirm you might need the GT1, but my issue was similar, and because 1/2 of the sensor was bad, it would shut close the lower rad hose - so it almost looks like the T-stat is stuck close, but actually the DME thinks the engine is cold, and prevents it from opening (just like when the external temp sensor is bad it shows -40°C, even if it's scorching hot outside, then your A/C won't work).

I have had my dash gauge freak out 2 or 3 times. it would get really freaking hot. happened right after start up or before pulling out of a parking spot.
cycling the ignition fixed it.

you may have had a stuck thermostat, but normally when they stick closed, they stay that way. yours sounds like it may have reset its self?

It's NOT a faulty t-stat.
Either it's the dual temp sensor or a bad Oil level sensor (yes it sounds stupid, but confirmed by BMW). read the link in my above post.

Can you explain for "cold" lower radiator hose, if indeed it is cold? Lower radiator hose is cold if there is no coolant flow back into the engine.

Yes, cold lower rad hose, when the dual temp sensor is bad, not only stuck t-stat. OP's T-stat is new.
I had probably the exact issue. Did you read the post I linked above? it explains everything. if the DME part of the dual temp sensor is bad, the DME won't allow the T-stat to open. But the other part that feeds the cluster will show the coolant temp (upper rad hose if you will - which is the high temp).

OK. When you say that it is not the thermostat, you are 100% ruling out the thermostat as one of many possible problems. I had thermostat go bad within six months so they can fail anytime. Anyways, thanks for the info link. Didn't know you can scan and open thermostat with GT1.

The GT1 will NOT open the T-stat (It will turn on/off a gazillion other instruments, lights, fuel pump, injectors, etc), but it will give you a T-stat specific code if it's bad. No other scanner will pick up that code. Only GT1, INPA, Autologic and the like. I am not sure an OE or Wahler (which is OE) T-stat will fail that quick, but I have seen stranger things happen. To rule the T-stat 100% out, one needs to scan for that T-stat specific code.
In my case, I did the cooling overhaul, and a few weeks later I had that same symptom the OP has. Also, the OP said he changed the t-stat. That's what my diagnostic was based on, which is NOT 100% accurate. If I were the OP, I would first scan to make 100% sure it's NOT the T-stat. I am 99% positive it will not pick up a T-stat related code, but this is internet diagnosis, so one doesn't see the whole picture......