The 2.3 liter and 3.0 liter take ( 5W-20 )The 4.0 liter takes ( 5W-30 )According to the 2002 Ford Ranger Owner Guide
one thing you have to remember is that all gasoline engines require GAS. so make sure you have some of that, and then it should start right up.
2002 models dont have an iat sensor
Flushing is best done at an oil change service center. ask your local service if they do it, or look in the phone book.
Older Vehicles (even up to 1998 or so) had external regulators but nowadays most all of them are "solid state" units and built into the vehicle's alternator.