To find it precisely:
1. Consult your owner's manual: This is the best resource. It will have a diagram showing the location of the thermostat for your specific year and engine.
2. Use a repair manual (like a Haynes or Chilton manual): These provide detailed diagrams and instructions for your specific vehicle.
3. Search online: Use a search engine with specifics: "20XX Ford E-250 [engine type] thermostat location" (replace 20XX with your year and [engine type] with the engine in your van, e.g., 5.4L Triton V8). Look for images and videos.
Important Note: Accessing the thermostat often requires some mechanical skill. If you're not comfortable working on your vehicle, take it to a mechanic. Incorrectly replacing a thermostat can cause significant engine damage.