Temp gauge not working

Long story short, I highly doubt the car overheated because it was -25* and the car had only been running for 10 minutes maximum, but my needle had gone all the way up to the red bar. As soon as it hit the read bar it dropped right down to where it would sit at running temp.
Since then the gauge doesn't work. Sometimes it'll move up a tad but drop right down a minute later.
My friend thinks it has to do with my coolant for some reason.
Any and all help is appreciated. The car is a '91 if it makes a difference. D15 with HF intake etc.
Since then the gauge doesn't work. Sometimes it'll move up a tad but drop right down a minute later.
My friend thinks it has to do with my coolant for some reason.
Any and all help is appreciated. The car is a '91 if it makes a difference. D15 with HF intake etc.
Comments
In the fall I had a rad hose burst so I'm 99% sure we mixed the coolant right. It's still a possibility. It would make sense, however since this first happened I've put at least 500km on the car. That one day it was warm I took a good drive and still no change in the gauge. I wasn't sure where to start, but it would make sense to me at this point it's electrical. If the rain holds off this weekend I'll try the connections and such.
On another forum a few members also said likely electrical.
Educate me though, how does the car get the temp reading?