Hey y'all, new member here.
I have a 2010 R56, about 55k mileage. Dad and I fixed it up two years ago and it's been my daily driver since.

Last week I noticed my radiator fan running after shutdown, it had done this before, but never this consistent. CEL came on, and stayed on. Advance Auto said code was P0136 for O2 sensor.
Prior to this, I'd the code, but it'd come on and go off on the next few startups.
Checked coolant, saw I was out, and didn't make it across ATL in time to get to BMW for blue coolant. Filled up with Zerex G05.

Drove it 2 miles to the train station for a few days, and fan would continue to run after shutdown. Drove home and parked it, noticed coolant dropped a bit. Jacked it up, rented a pressure tester, pressurized to 15. Appeared to hold pressure, did not see any leaks below, when wiggling hoses a bit pressure also held. There is a small puddle to the drivers side of engine below two hoses, so possibly a small leak from the clamp?

Unjacked car, battery would not start... Flashed a bunch of indicator lights. Charged it up a bit, went to work next day. Returned pressure tester, filled up with gas and threw in some cleaner as a shot in the dark. Parked at Advance, heard fan running, tested codes, received P0136 still, as well as P112B (low coolant?). I had filled up to the max level, and erased the codes to see if they'd throw again. Car didn't start again. Jumped by roommate. Got home, tested the AC and it blows cold, but fan does not immediately turn on, about 30 sec later it seems the high powered option runs. Heater blows warm.

Charged it overnight, drove to work this AM, fan did not run after shutdown... will get battery tested tonight as well.

Any ideas what this could be?
Will monitor level and if it continues to drop, I will have to get it checked out. The small puddle to the right concerns me, as did the fan running afterwards after short distances, and the battery failing.
initial thoughts were low coolant but I've refilled. Fan running leads me to believe a failed thermostat from the low coolant, but what would explain the puddle, but no loss of pressure?

 

Here is a test..... with a cold engine... start the car and shut it off.... if the fan continues running for several minutes the temperature sensor in thermostat housing has failed hard on "hot". Mine just did that recently... throws a code and makes the care run very weird as the computer thinks the engine is hot when it is not.... very noticeable when trying to run and drive in sub freezing temperatures... made a huge difference when it was replaced. Good luck!

 

I believe that 2010 is still in the range of years for the thermostats that go bad. It often happens at ~60K, so you're a little early. The thermostat is on the driver's side of the engine, and when mine went it leaked coolant a little. I don't remember it being as fast as you're describing, but you may have had an air bubble in the system when you added coolant, and part of the drop was just the system working that bubble out.

 

failed primary O2 sensor can make ECU think that the EGT are waay out of spec, which could act like a temp/overheat..

*swapping out the O2 is a bit easier than replacing the thermo housing.. but both are worth looking at for certain.

 

Temp sensor failed or you have slow coolant leak and its letting air get in the system. I would bleed the crap out of it first. Which can also trigger that. Took me about 3 cycles to bleed it all out.

https://www.northamericanmotoring.co...ugh-start.html

Check that socket also:

https://www.northamericanmotoring.co...epairable.html

If you see coolant on top of the transmission or leaking down the back its the thermostat:

https://www.northamericanmotoring.co...8-no-heat.html

Thats pretty much all the things to check with the above mentioned.

 

@Dmyer:
I drove home 2 miles and got home about 6:45. I just popped her open to check, it is 9:45. I could sense it was just a bit warm under the hood yet, but after 2 miles, I would have thought three hours would do the trick.
Coolant tank release a tiny amount of pressure yet, which also told me still warm. Filled coolant up about 1/4 inch.

Turned it on, 5 sec later turned it off. No fan running. However since I cleared codes Tuesday, it hasn't run at shutdown.

 

 

 

 

Yep, thats its, the thermostat dripping and pooling on top of the transmission.

 

My suspicions, unfortunately... Anyone know of a good shop here in ATL?
I could attempt this myself, but it'd be the first major job I've done (I'm a young buck), and not sure if time is on my side until this weekend.