Where is the thermostat on a 1987 f250 6.9l diesel?

The 1987 Ford F250 6.9L diesel doesn't have a thermostat in the same way a modern car does with a user-adjustable dial. Instead, the engine's cooling system temperature is controlled by a thermostat located in the engine block itself. You won't find a separate housing or easily accessible dial. To access it, you'll need to:

1. Consult a repair manual: A Haynes or Chilton manual specific to your year and model will have diagrams and instructions showing the thermostat's location and replacement procedure. This is crucial because engine components vary slightly from year to year.

2. Expect some disassembly: Getting to the thermostat requires draining some coolant, and likely removing some components like hoses and perhaps the water pump or fan shroud. This is not a simple job.

In short, there's no readily visible thermostat like in a car's cabin. It's an internal engine component requiring mechanical knowledge and tools to access and replace.