With engine at idle, when it hits normal operating temperature.
Is the main fan turning fast?, if not, the fan clutch may be bad.
Try changing the thermostat, it is cheap (about $20.00). It may be sticking in close position.
If the above doesn't work, your water pump may be going bad.
Those are possibilities, diagnose before purchasing expensive parts.
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car