Audi A3 OVERHEATING

Driving a 1.6 cc engine Audi A3 I noticed the temperature exceeding90 degrees to 120degrees on the engine temperature gauge
we knew there was water being brought back to the expansion bottle as the small pipe was flowing back water and the water pump and timing belt done at 118.000miles.
green coolant switch was replaced and themostat housing. Also at 110 degrees the fan cuts in but not all the time,
no water is being lost as we do not need to replenish with coolant.
in traffic at 110degrees when I put the heating switch from cold to hot on the interior heater the temperature drops to 90 in less than a minute on the temp gauge
when the interior fan is switched off the temperature exceeds 90 degrees again,
and when we adjust the interior temperature back to the cold position the temperature exceeds 110 degrees on the gauge