To be certain, consult your owner's manual. This is the most reliable source for your specific vehicle. If you don't have the manual, you can often find a digital copy online by searching for "1987 Ford Ranger owner's manual PDF".
Failing that, check the radiator and overflow tank for capacity markings. Adding up those capacities will give you a close approximation. Remember to add coolant to the radiator and overflow tank to the proper levels.
