Engine Overheats With External Coolant Loss

Broken or slipping fan belt.
Thermostat stuck closed.
Water pump shaft broken.
Leaking freeze plug(s).
Faulty fan clutch.
Faulty electric fan motor.
Faulty thermal relay switches.
Faulty radiator pressure cap.
Water distribution tube clogged.
Radiator air flow passages blocked.
Incorrect ignition timing.
Faulty distributor vacuum advance unit.
Exhaust system restricted.