* Coolant Temperature Sensor (CTS): This is the one most commonly referred to as the "temperature sensor". It's used by the engine control module (ECM) to regulate fuel mixture and other engine functions. Its precise location varies slightly depending on the engine configuration, but it's usually in the intake manifold or directly in the cylinder head, near a coolant passage. It's a single-wire sensor.
* Sending Unit (for the gauge): This sensor is responsible for sending the signal to your instrument cluster gauge to show the engine temperature. It's also located in the engine block or intake manifold, but is often in a different location than the CTS. This is a two-wire sensor.
You'll need a repair manual specific to your 1986 Chevrolet 350 G30 van and its specific engine (e.g., a 5.7L small block V8) to pinpoint the exact location of each sensor. A diagram in the manual will be invaluable. Looking at the engine with the appropriate diagrams will help you identify the sensor(s). Be careful when working near hot engine components.
