Chevrolet Matiz 2006 Overheating?

my matiz has been brilliant for the last 5 years, no problems.
but its recently started overheating and the mechanic cant figure out what the problem is.
he had checked the h.gasket(its not that)
he has checked for leeks...its not that either
he checked for water coming out the exhaust...not that either.
could someone advise please?
Eileen, February 2012


done
thermostat?water pump?

cdc, February 2012
thermostat?water pump?blocked radiator?

cdc, February 2012
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