I only know of four things that can cause a car to overheat: head-gasket, radiator, fan, thermostat.

1. I check the oil to see if it was contaimated with antifreeze. it was ok.
2. cut the car on and fan was ok.
3. radiator appear to be holding the antifreeze.

I am guessing it's thermostat but I am curious what else it could be.....

Which engine do you have?

Can you elaborate on the symptoms? Does it overheat when moving, or just when sitting still. Does having the AC on or off make a difference?

radiator cap

Also the radiator could be clogged, as could the heater core, or really anywhere in the system, but those 2 things can clog up and cause problems.

yea it must be a clog radiator because the car thermostat temp gauge drops up and down.

yea it must be a clog radiator because the car thermostat temp gauge drops up and down.

If the engine temp seems to vary alot, I'd replace the coolant temp sensor first to make sure the gauge is accurate.

Most likely it's the thermostat. I would change it and flush the system out.