Hi guys, Need your opinion and suggestion on this. Here's the deal and I'll try to make it as detailed as possible. Bro in law drives an A3 1.8T 2001 model(AUM engine) and on the way to work, the coolant temperature sensor's flange(only found out at a later stage) decided to crack and the engine over heated. He filled it up with some liquid based(copper me thinks) stop leak and coolant and returned home. Somehow the leak stopped but a day later it was revealed that the said flange had a hairline crack. Got a new replacement, replaced it and went for a test run. When the engine's warmed up, I let the in law drives it, with me inside the car and the temperature suddenly went up, even when there's air going through it(at speed). There's no external leak whatsoever found/noted. I noticed the fan not running into the 2nd speed(cut in at 97c)..since the fan is running after all, I was thinking the thermoswitch at the radiator's end tank at fault. Again, got a thermoswitch as well as the thermostat new replacement part which my bro in law says doesnt mind replacing it just in case, after all the engine is about 9 years old now. Before replacing them, I reverse flushed the radiator to remove at the sh*t*(if any) inside. I even reverse flushed the engine. Ok, after fitting the new parts, filled with coolant(green stuff), went for a test run. To my horror, the temperature still goes up! So i consulted a friend who works on european cars and told to check the cooling fan's speed if they're fully functioning..he also mentioned something about a relay board/fan control unit located somewhere on the passenger side's chassis rail that have failed. Reached home and tested the fan on both speed and it was ok. I consulted local audi forum members(ozaudi) and a member pointed to me check on the water pump. Engine warmed up, squeeze the upper hose and feel if it swells. It did. For now, I would assume the water pump is ok. As the fan is not kicking in into the 2nd speed, I would think the fan controller unit was faulty. Again, bought a new replacement controller unit and waited for it to kick in. Now, the fan stopped working completely! Im all buggered trying to figure out why as I was not rough with the wiring loom to the fan controller unit. Im gonna trace some wires/connectors now just in case. Waiting for you guy's opinion and suggestions on this. Danny. edit: it it got me thinking, if the car is at speed, there's air going through it, there's no need for the 2nd speed to cut in. Furthermore, maybe I did was pretty crude, I sprayed water(shower) in front of the car's grille to get some water to get rid of some heat from the radiator. As a heat exchanger it should work but it didnt. So what do you guys think? I havent pressure tested the cooling system but so far the car idles well, no steam/white "smoke" coming out..