Check the compression (or have it checked).

If you have good compression then the odds are *very* good that you have
a good head gasket.

If you have bad compression it might mean a problem with one or more of
the following:

 head gasket
 valves
 rings

I'd expect a bad head gasket to also cause one or more of the following:

 water in the oil
 oil in the water
 exhaust gas forcing the coolant to leak out of the coolant overflow

Overheating at idle could simply be a cooling system issue:

  fan not working
  reduced radiador function (ie: bugs in radiator)

Possible, but I doubt it. Head gasket problems, especially those related to
overheating, tend to get a lot worse when the engine is under load - that
is, when driving. The higher combustion chamber pressures force more
combustion gasses into the coolant. If you want to do a quick test, remove
the radiator cap when the engine is cool. Start the engine, pinch closed the
tube that goes to the coolant reservoir, and put the palm of your hand over
the radiator cap opening. If you feel either a pulsation or a steady rise in
pressure on your palm immediately, that's bad news. If not, you can bet the
head gasket (or a cracked head) is not causing your overheating.

My main thoughts are just the sort of things Jim mentioned - things related
to either coolant flow or air flow.

Mike

hi,
Thanks for ur responses, i would take the car to a different mechanic and
check for the thermostat and radiator.