Temp guage on 95 940 doesn't work. Multimeter reads infinite resistance across coolant temp sensor, telling me it is open. Removed connector and shunted 80 ohm resistor across it..temp guage red 1/2 way, or normal. I am sure sensor is my problem and needs replacing.

Questions:

Must I drain the coolant below sensor, or can I slowly unscrew the old one and quickly screw the new one in and lose only a small amount of antifreeze?

Is there a washer or o-ring that I need to order along with the sensor? If not, is it advisable to use teflon tape on the threads or maybe anti-sieze?

Your experience and advice greatly appreciated.

thanks