My engine is overheating why?

Do you have a 2valve or 4 valve per cylinder engine?

White smoke from exhaust on start up? Oil look normal?

Is the noise constant? Does it change when slowing down or accelerating?
If not, and it is intermittent, it could be the thermostat.
It could be the head gasket is blown.
You could change the oil and look for a millky white colored liquid which anti-freeze.

Has the performance of the car changed since this started happening?
Does the exhaust smell like anti-freeze? Any puddles under car?

Next time you get a chance, grab the upper radiator hose after driving. It should have pressure that you will be able to feel.

Few thinks need to be checked
check radiator /coolant fan going on when needed
and if coolant circulating through
check water pump
check headgasket

Remove the distribution box and position aside. See Fig. 1 . Disconnect the fan electrical connector and detach the retainer. Remove the bolt and the electrical cooling fan. See Fig. 2 . To install, reverse the removal procedure. Tighten bolt to specification

If its not overheating and the Stat is okay-check and test the coolant temperature sensor and the engine temperature gauge sender could be out of calibration

Have it block and pressure tested-do the block first to pinpoint a combustion leaking into the cooling system or a gas analyzer to sniff for hydrocarbons at the radiator fill neck.

Pressure test: do not do a pressure test if there's leakage at the headgasket this might cause coolant into the cylinders and lock it up or bend a connecting rod if cranked thereafter. The headgasket should be repaired before doing the pressure test.

If the block and pressure test passes check the following:, Pressure test the Rad. Cap, Clogged radiator, air lock in the cooling system, Fan clutch, Radiator electrical fan, collaspe hoses, water pump.