Partial list of Possiblities:
Body damage or Modification causing air flow problem
Water pump has internal Damage.
Air pocket in the cooling system, many cars require a special Purge Proceedure.
Blown head gasket or Cracked Cylinder head. A Good Repair SHop can test for this quickly and easily.
Bad or faulty cooling fan.
If the car has a cooling fan clutch they fail also.
And many other reasons.
first of all, do you have the right thermostat? ie: winter, summer. if so i would get the radiator checked, it may be getting pluged.
Check the fan thermostat.
If the coolant is brown, it has broken down and needs replaced. You could also have a failed thermostat, plugged radiator, inoperative fans,...........
Bad thermostat, plugged radiator, blown head gasket in order of expense.
Low coolant, stuck thermostat, failed waterpump, plugged radiator, inoperative radiator fans, etc.
U NEED A THERMOSTAT. THAT IS WHAT HOLDS THE COOLANT IN THE RADIATOR, SO IT CAN COOL DOWN BEFORE IT GOES BACK IN THE MOTOR.
Assuming it did not overheat before you replaced thermostat and water pump you may have installed the thermostat backwards. It is also possible the cooling system wasn't refilled properly and was air bound.
because the water pump is not working properly....
low coolant ,froze thermostat ,leaks in hoses ,radiator
i would have replaced water pump long before replacing radiator. also check engine oil to see if it has engine coolant mixed in.if it has then the problem is more likely to be a bad head gasket
If the electric cooling fan(s) are not coming on that may be the problem.
Here are a couple possibilities. Thermostat in backwards(spring goes toward engine),plugged radiator,radiator hose collapsing, bad head gasket. Hope this helps