Changed the thermostat, but it still over heats?
you need to back flush your motor by removing the bottom hose and top hose and feed water into the bottom and a load of muck will come pouring out the top, also try water pump and head gasket, does the heater blow cold when you are not moving and motor is warm, you local technician at your local shop should be able to diagnose and fix the problem for at most $200
If flushing the radiator and engine does not fix it then you probably need a new radiator.
Search Ford Ranger Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Ford Ranger Experts