Look for a sensor with one or two wires connected to it, often near the thermostat housing or in the intake manifold itself. It's usually a threaded sensor that screws into the intake.
To find it, try these steps:
1. Consult a repair manual: A Chilton's or Haynes repair manual specific to your 1984 GMC Sierra 350 will show you a diagram with the exact location. This is the best and most reliable method.
2. Examine the intake manifold: Carefully inspect the intake manifold, especially near the thermostat housing. Look for a sensor that looks like a temperature sensor; it's often a cylindrical device with a wire or two attached.
3. Trace the wires: If you can locate the wires going to the coolant temperature sensor connector (often near the engine harness), you can follow the wires back to find the sensor itself.
4. Look for a temperature gauge sender: Note that there's also a sensor that feeds the temperature gauge on your dashboard. This is *not* the same as the coolant temperature sensor (CTS) used by the engine's computer (if equipped with fuel injection). The CTS is typically a smaller sensor.
Important Safety Note: The engine and its components will be hot after running. Let the engine cool down completely before attempting to locate the sensor.
Without seeing your specific engine, it's impossible to give a more precise location. Using a repair manual is strongly recommended.
