There are a handful of possiblilities. T-stat is one, too weak of antifreeze, leak/low coolant, internal plugging, cooling fan not working off the top of my head.
If your car is over heating you may want to check your thermostat and replace it may solve your over heating problems
Leaking isn't the only thing that can cause overheating in a car. It's possible that the thermostat has gone bad and needs to be replaced.
If you suspect the thermostat is no good, replace it with a new one, don't leave it out.
thermostat help fan come on when the car is runnning, keep the engine from over heating
You need to have a shop check your radiator cap, water pump, cooling fan and thermostat for proper function...the most common cause for over heating is a thermostat that has gone bad and is stuck closed not allowing the coolant to circulate and cool the engine.
If it is not actually over heating, then if the smell is outside the car, look for coolant leaks around the head and the thermostat cover. Inside the car could be a leaking heater coil.
it can be many stuff but in your place i would check first the coolant level and the thermostat
If your radiator isnt leaking and car is having a over heating problem and coolant spewing out. Chances are your thermostat needs replaced. possible the radiator needs to be flushed. But more likley its thermostat
I am not familiar with the Audi, but on most cars, the thermostat is at the point where the top hose leaves the engine to go to the radiator. A bad thermostat can make your car overheat. If it has not been changed since 1992 it should have been changed long ago.
If you need a heater core, the one you currently have would be leaking. If the car is over heating or not getting warm enough, think thermostat.
IF YOUR CAR IS HEATING UP(OVERHEATING) AND YOU STILL DRIVING IT, A FAULTY THERMOSTAT IS THE LEAST OF YOUR PROBLEM.
Change your thermostat!