You absolutely MUST check your owner's manual. This will tell you the specific weight and type of oil recommended by Ford for your *particular* Bronco engine.
However, generally speaking, for that era, you'd be looking at:
* Oil Weight: Likely something in the range of 10W-30 or 10W-40. Again, check your owner's manual for the exact specification. Using the wrong weight can severely damage your engine.
* Oil Type: Conventional oil was the standard back then. While you *can* use synthetic oil, it's not strictly necessary unless you're experiencing issues or wanting to extend drain intervals (though in an older vehicle, that's less crucial). Modern synthetic blends are a good compromise between performance and cost. Do not use high mileage oil unless your Bronco has extremely high mileage and is experiencing significant oil consumption. Look at using high zinc oil (if you use classic oil) to better protect your engine's components.
In short: Find your owner's manual. That is the ONLY reliable source for the correct oil type and weight for your specific 1987 Ford Bronco.
