External temperature too low

Hello.
has a 90s V8, so still the old climate display. My external temperature has always shown me values of -7 degrees for a few days. I used to install a digiatle thermometer with a probe. This always shows me values of approx. 0 degrees. What kind of feeler is broken here? The front of the cooler or the one in the waterbox? Is there any way to measure them for resistance?
Thank you very much.