To be certain:
1. Consult your owner's manual: This is the best source for the exact location and instructions for your specific vehicle.
2. Look for the radiator: The coolant reservoir is almost always near the radiator. Once you find the radiator, look around it for a plastic container.
3. Check online resources: Search for "[Year] Chevy Astro Van coolant reservoir location" on Google Images or YouTube. You'll likely find pictures or videos showing the location.
Important Note: Never open the radiator cap when the engine is hot, as the pressurized coolant can cause serious burns. Always let the engine cool completely before checking or adding coolant.