Could be low on coolant or a faulty thermostat.
because your thermostat is opening and closing as the engine temp. fluctuates
If your temperature gauge isn't working the problem is a bad gauge, grounded or disconnected wiring or, most likely, the temp sender isn't working.
Could be lots of things. You should have it checked for codes. The temp gauge problem would make me think of a possible temp sensor problem. It should be located near the thermostat housing.
To fix the temp gauge check the temp sending unit first. A bad sending unit is a common problem with the temp system.
If the temp gauge no longer works then either the gauge itself has failed, the sending unit has failed, or there is a problem in the circuitry.
Thermostat stuck open or no stat at all. Faulty temp sensor or Gauge.
why doesn't my rpm gauge and temp gauge, fuel gauge not work
Becasue it is icey out?(:
Check ignition switch
Replacing the gauge could be a costly job but it is seldom the gauge goes bad. More likely the temp gauge sending unit is at fault. Replacing the temp gauge sending unit would take less than 15 minutes.
Because they are broken is one reason
You temperature gauge could be not responding because of a faulty fuse. If you check your fuses and they work then you may have an electrical problem.