* On the intake manifold: This is the *most common* location. The sensor is usually screwed into the intake manifold itself, near the thermostat housing. It's often a single-wire sensor.
* In the engine block: Less common, but possible. It would be screwed directly into the engine block, usually near the thermostat housing.
To find it definitively:
1. Consult a repair manual: A Haynes or Chilton manual specific to your 1991 Chevy Lumina with the exact engine type (e.g., 2.5L, 3.1L, 3.8L V6) will show you a diagram with the exact location. This is the best approach.
2. Visual inspection: With the engine cool, locate the thermostat housing. The coolant temperature sensor is usually nearby, often screwed in and connected by a single wire. Look carefully around the intake manifold and the engine block near the thermostat. The sensor may have a single wire or a few depending on the type.
3. Use a thermometer to check the temperature: Start up the engine. If the car’s temperature gauge is not working then you're trying to find this for a reason. Once the engine has run long enough to show a change in temperature use a meat thermometer on the radiator hose and engine block to check the temperature of the coolant.
Remember to let the engine cool completely before attempting any work near the engine. Hot coolant can cause serious burns.
