Low Coolant or faulty gauge
your coolant level could be low
THere are 2. one for the gauge, and one that reads for the fan. the gauge one is located by the firewall, while the other is near the coolant thermostat housing.
If the temp gauge reads normal and the engine is not overheating, the thermostat is doing its job. The thermostat maintains the coolant temp by opening and closing allowing the coolant to flow or not to flow. When it is closed the coolant doesn't circulate.
If your coolant level is fine , it sounds like your thermostat is sticking open
Either your engine coolant temperature is HIGH , your oil pressure is LOW , or your fuel gauge reads at or near empty
You might plan to refuel when your fuel gauge reads one-eighth of a tank of gasoline. Some people choose to refuel when the gauge reads one-quarter of a tank remaining.
Temperature gauge reads signals off the coolant temperature sensor. It can also point to a faulty thermostat. If your car runs rough in cold, idles rough and uses up more fuel then coolant temperature sensor is your problem. They are normaly a cheap and easy diy to do.
Usually there will be a repeating chirping noise during engine running, also your tempurture gauge reads hot . with me, i was leaking antifreeze/coolant, but not all the time
i just put in a new radiator and now temperature gauge reads high but their are no leaks
any make after 1997 will be susceptible to electrical issues when engine is normal. i wish they would have left the computer stuff out of vehicles. gauge is most likely electrically impaired.
Connect a gauge and freon can to the AC low side port of the A4. With the engine running and AC on high, open the freon valve and allow coolant to flow into the system. Turn it off when the gauge reads full.