I replaced my thermostat at the weekend for a couple of reasons, firstly as the temp gauge wasn't going over 70 when driving, and secondly the radiator fan wasn't kicking in - ever. It's an A4 1.9tdi 2003. Bled the coolant properly, no signs of airlocks etc. New thermostat in, and the coolant sits dead on 90c once the car is driven a few miles. Never rises above 90c, vents put out hot air, MPG seems about right etc. Nothing untoward at all. Except the radiator fan (unless I miss it happening) never seems to come on. I'm used to, in my previous cars, having the fan over-run for a little bit once I reach my commute destination (mix of traffic jams and motorway). But in the A4 it's never running when I stop... does the A4 tdi run really cool naturally? I checked the rad hoses, top one is hot, bottom one was very vaguely luke warm, expansion tank pipe was hot too. All the pipes were nice and soft and not rock hard over pressured. What temp is the radiator fan meant to kick in at? It's getting up to a solid 90c after 5-8mins or so of driving, with another 20-25mins of driving after that before stopping. Options are an impeller-less waterpump, or a duff fan connection/switch/fuse. But the solid 90c and cold bottom pipe is confusing me as I'd have thought it would have overheated in those circumstances?