Oldsmobile, Silhouette, 1990, Temp guage not working.?

Simple circuit, simple diagnostics. Locate the proper temp. sensor on the motor as there are two. One for the PCM temp. input and one for the driver's guage. The PCM has two wires going to it and the guage has one. All you have to do is unplug the guage from the sensor, turn on the ignition and look at the guage. It should either be at cold or over the hot mark. Now ground the guage wire to the block being sure that it is grounded and re-inspect the guage reading. It should be opposite of the open. If it does both of these functions, the wiring and the guage are responding. Usually we would install a new sensor into the block to see if that is the problem. Since you have already done this and are sure it is not the problem, you have a faulty dash guage. I think these require a complete dash embly which is pricey. Good luck.