Thermostat Housing & Temp Sensor (@elbow)
 

Greetings. 2012 r56 Base/Manual. Seemingly overheating?? Can a new H2OTempSensor be bad? While having the clutch replaced at a Shop, I had them replace water pump and original H2OTemp sensor located on elbow near (not on) Thermostat Housing. ODBII indicates temp is now 230degF and rising when driven. Shop says car is too hot now, they blame the fact that I'm using Evan's Waterless Coolant; been using Evans for 2yrs no OverHeat issues. So I get Mini home and I replaced Thermostat Housing. New Housing unit has split adapter and connects to another H2OTempSensor?? However, the TempSensor on the elbow is still tied to the ODBII reading/output; when I unplug, the ODB reader stops reading. I'm pretty sure I've bled the system properly. I put a thermocouple on surface of elbow near replaced H2OTS location and a thermometer dipped into the coolant reservoir, both read 64dC/150dF; this seems low. I can't imagine the thermodynamics of Heat Transfer would loose 80defF between interior liquid and surface. Can't find anything on new Thermostat Housing and why the wiring split and what it all does; what is the new (added) sensor (H2OTS??) on top of the Thermostat Housing?? Is there an ODBII line to read this sensor? I've ordered a laser temp reader to see what it says about the engine. So...
Can a new H2OTS (on elbow) be bad? What is the new sensor on top of the new Thermostat Housing?? Thanks All.

The symptom you described sounds more like the T-stat won't open accordingly, sensor seems to be okay.

If you got a new thermostat housing, there's a thermostat switch on the back side, this switch is integrated into the housing itself. My bet is that the housing you bought could come with a bad switch. The temperature sensor should still be okay since it can read temperature rising. Not sure where do you buy the thermostat housing, but if it were me, I'd make sure to get the OEM part just because of how critical it functions in the car.

The Thermostat issue resolved
 

Thanks. As it turns out, the new Thermostat Housing came with it’s own sensor; it has two plug-ins now vs one. The new dongle did not have clear directions and it appeared you just plugged it in at the connection for the elbow temp sensor and then plug the two new plug ends on the old elbow sensor and the added sensor on top of the new Thermostat. This created a skewed reading by the engine computer thinking it was hotter than it was and shutting the car down at 245deg. Laser temp reader indicates the engine was 165-212deg depending on where you pointed.
Bottom line: the new dongle replaces the original OEM dongle, not plug into it. The elbow temp sensor (aka: fan switch) is abandoned for the new placement on the Thermostat housing.