To test the temp guage; pull the wire off the temp sensor, the turn the ignition to the on position. note what the temp guage reads. Next, take a test wire and connect it to the wire that you just took off the temp sensor, and connect the test wire to a good ground. If the temp guage moves, you temp sensor is bad. If it is still stuck on 140, you have a bad guage. What you are doing is creating an open circuit, then a grounded circuit, one should make the guage read cold and the other should make it read hot. If it dosen't move at all you have a bad guage. Hope this helps!