You don't mention the engine size, but on the 3.1L V6, there are two temp sensors. One operates the guage on the dash, the other is the temp signal for the ECU to help control the air/fuel ratio. To find them, let me try to navigate you through the engine compartment of a 3.1 found in a 1994 Corsica, which should be exactly the same. If you are confident enough to replace the temp sensors, I will assume that you know most major items on the engine. The v6 sits "sideways" under the hood, so there will be a front head and a rear head. The guage sensor is located on the front head, near the transmission. If you locate the upper radiator hose coming from the drivers side of the radiotor and follow it to the thermostat housing on the rear of the engine, you should find it just to the left of the housing, it looks to be made of brass, and I believe there is a single wire coming out of it. The ECU sensor is quite a bit harder to find. It sits on the the very corner of the "rear" head, closest to the transmission side, also with a single wire, maybe even green. It is pretty hard to get to without taking the EGR assembly, and thottle body out. This is all pretty vauge, I know, but it's the best I can do since I havn't been in a 3.1 for a couple years. All this info is under the assumption that it is a 3.1, and its similar to a Corsica. If the ECU sensor needs replacing, it most likely is giving a code and Check Engine light. If the guage sensor needs replacing, then the guage probably is not functioning properly

