Needed to drive across London today using the heater on full to keep your temperature lower on my small 944. Got stuck in certain traffic initially when i first observed the temperature gauge did not visit midway around the dial enjoy it usually does. Have checked coolant levels and they're fine, even the radiator fan takes over if this should. I am speculating it's apt to be the thermostat or even the water pump not circulating the coolant effectively.

Any ideas?