I wrote a paper on how to bench test the temp and oil pressure gauges. You need a variable resistor. I think I used two. A 100 Ohm and a 500 Ohm. The variable resistor takes the place of the sender. The bench testing process will validate whether or not your gauge is resgistering accurately or not.
If you want to test the gauges in the car, for the temp gauge, remove the wire to the sender. The gauge should drop to zero (with the key on). Then ground the sender wire to the block. With the key on, the gauge should read way over to the right. Same process for the oil pressure gauge, expect ground and unground positions on the gauge are reversed.
If you don't get those readings, then you'll need to pull the cluster and check the back circuit for breaks. Usually problems are circuit related rather than a bad gauge. The oil and temp gauges share the same 12 volt circuit. The oil pressure gauge is first in the circuit, then the temp gauge. So, it's possible to have a break in the circuit between the two gauges, whereby the oil pressure gauge works but the temp gauge doesn't (this happened to me). If that's the case, you can run a jumper between the two gauges because there are nuts at the place where 12 volt enters both gauges.
You may have a grounding issue if you have problems that appear over various gauges. The brake lights share 12 volt with the oil and temp gauge, and the cluster lights share ground with the gauges.