Sorry, I meant to say the brown m20 coolant temperature sender.
After looking at some write ups, I realize that my m52 obd2 head will not accept the m20 coolant sender. My options are to rethread the sender to the proper size or buy one that is made to fit from the link below.
"You will need to use an e30 brown top coolant temp sensor for the cluster reading. This will replace the pipe that screws into the head for the throttle body coolant line. You have three options here
Option 1 (what I did): Use a die and change the pitch of the threads to match the s52 head threads. The pitch was m12x1.5 (could be wrong, double check)
Option 2 (more risky IMO): Tap the head to match the sensor threads.
Option 3 (expensive, but easy if you don't have the tools: Buy a already rethreaded brown top coolant sensor from Markert motorwerks. http://www.markertmotorworks.com/MMWProducts.html"
Full write up here