The reason you need to determine this for sure is that it affects "what might be wrong"
For a "quick check" do this:
Go out and find the temp sender on the engine...........what engine do you have? Remove the sender wire, and ground the wire to the engine with a clip lead. Turn on the key and watch the temp gauge. It should peg in a very short time. Do not leave the key on any longer than you need to find out
