Where is the thermostat located on a 1987 Ford E150 Van?

The thermostat on a 1987 Ford E150 van is located under the intake manifold, on the engine block. To access it, you'll need to remove the intake manifold. This is a significant job requiring mechanical aptitude and the right tools. It's not a simple "pop the hood and there it is" scenario. A repair manual specific to your van's engine (e.g., a 302 V8, 351W V8, etc. – check your vehicle's documentation) will provide detailed instructions and diagrams.