If you can crawl under the dash,check to make sure the black wire from the voltage limiter going to the temp guage is plugged in.
If it is plugged in,pull it and with a multi meter with engine warmed up,and key "on" but not running see iff there is 5 volts pulsing from the black wire.
From there plug the wire back in.under the hood check for juice going to sender. should be pulsing up & down 5 volts.
Check that wire all the way to the bulkhead for any damage.
If you have juice going to both the sender and gauge but no reading replace gauge.
I am assuming the other guages (fuel,oil) are working since they share the same feed from the voltage limiter.
Hope this helps