Good Afternoon.

I've recently had a problem with leaking coolant in my 2011 R55. It only would leak coolant after cooling down, and I believed it to be my thermostat housing. After replacing the thermostat housing, everything seemed okay, but soon the dribbling continued. I've located it to a coolant elbow below the air intake pipe from the filter to the turbo, between the coolant reservoir and the engine seen here.




Now, I'm pretty sure it's coming from the senor seen below, as evidenced by the sediment left from the coolant around it. I've pulled it out, tried cleaning up the seal, but it still dribbles as it cools down. I would figure on a complete replacement on the sensor, but as I don't even know exactly what sensor it is, it's hard to figure out. I understand the real temp sensor is located in the thermostat housing (or that's what I've understood), or was this made redundant with the new one?

 

Info on the CTS sensor in that elbow is here: https://www.northamericanmotoring.co...ml#post4268233. Let me know if you have any questions or need the replacement part for it if you have the new t-stat with the CTS integrated into it.

 

Remove the sensor and clamp the hose at either side of that elbow, clean the sensor and mating surface really well with brake clean, make sure everything is dry and apply a bead of black RTV around the coolant temp sensor and reinstall. Let the RTV set up before you introduce coolant to the area, but it will never leak again after that.

When the time comes to install a new thermostat it'll have a temp sensor in the housing, but the old thermostat design uses that external sensor. Once you go to the new thermostat that sensor will become a glorified plug, no wiring goes to it anymore.

You could buy the updated elbow, but just sealing it with the RTV will keep it from ever leaking and is cheaper than buying the new elbow.

 

does the coolant need to be flushed before doing the rtv fix? And if not, is the coolant exposed when pulling off the sensor during the cleaning? I’m worried about there being risk of contaminating the coolant or getting too much air into the system but am not sure if those are valid concerns.