Where is the coolant temperature sensor on a 1991 Chevy Corsica?

On the 3.1 Litre V6 engine ("T" Vin Code) the sensor is on the Left-hand side of the rear cylinder bank, above the exhaust manifold and below the valve cover. It is not the Wells' SU109 part, and least on our 1991 Corsica LT V6. We're still trying to find the right part. Chevy wants about $50 or so for it. Aftermarket for the SU109 was only $10! ***** Well kinda, actually I believe that the question asked, specified "sensor" and that is located in the thermostat housing on the left side of the motor under the thermostat, that component is actually called a "coolant temperature sensor". On the 3.1 Litre V6 engine the "coolant temperature sending unit" is on the Left-hand side of the rear cylinder bank, above the exhaust manifold and below the valve cover as mentioend in the previous answer. Although the question asked did not mention as to why you think you need to replace this. As well as the person first answering the question may be needing the proper solution if the sensor they bought was the wrong one. Or did not seem to fix the problem. I will answer a frequent misconception about these units and add yet another. Since many people are pointed to these items in hopes of repairing the LOW COOLANT Indicator Light which suddenly came on in their instrument panel. Now if this is the problem your trying to resolve, these other components are probably not what your looking for. Since one controls the COLD/HOT guage on your panel and the other causes your radiator fan to kick on and off. Allow me to introduce the proper part for that problem. This is only a ($12.00) Twelve dollar part which the parts stores and repair shops wont inform you of, until after you've allowed them to overhaul your engine or you've already purchased all of these other sensors and sending units first, which ranged from 25 to 85 dollars on average... NAPA Auto Parts sells a component and their part number is FLS609. It is called a Fluid Level Sensor. It is a unqiue little sensor with two prongs at one end. This unit simply pops into the external housing area on the lower pocket on the outside of the Coolant Resovior Tank (bottom side facing the engine). It has a quick release plug and may look tricky to get out because of the space and location unless you remove the tank entirely. But there really is no need to remove the tank. After disconnecting the negative battery cable, remove the bolt on the upper side of resovoir tank where it connects to the fender wall, pull the tank back and up carefully until you can access the unit on the underside. Simply unplug the bad unit, insert the new sensor and then plug it in. re-connect your battery cable and turn on your car. Your motor will made a few wierd noises, clicks and whirrrs, and will begin to idle high for a moment and then resume to be normal. Your LOW COOLANT incator light on the instrument panel will no longer be lit up. Good Job, Well Done. Happy Motoring