* On the thermostat housing itself: This is a more common location. The sensor is often screwed directly into the housing.
* In the engine block: This is less common, but possible. It will be a sensor threaded into the engine block, usually near the thermostat housing.
To be certain, you'll need to consult a repair manual specific to your 1995 Chevy Astro van's engine (4.3L V6 is the most common). A repair manual will have diagrams showing the exact location and appearance of the sensor. You can often find these online (for purchase) or at your local auto parts store. Looking at online forums dedicated to Chevy Astros might also yield images from other owners that could help you identify it.
Before attempting any repairs: Remember that the coolant will be hot. Allow the engine to cool completely before attempting to locate or replace the sensor.
