Audi 5000/100/200 cooling system....
 

TOTLY S#@KS!!! A bazillion thermoswitches, sensors and relays and it still doesn’t work right. Just like anything German it is overly complex and failure prone. Having worked for a German manufacturer I can say that this philosophy goes beyond just cars. While the radiator is more then capable to remove the heat, it is placed behind the headlight assembly so there is no direct airflow. Instead air is redirected through cheesy deflector/air-box that doesn't survive the elements, expensive and practically impossible to replace. I tried to find one at local junk yard and guess what, they are all thrashed! To change the stupid thing you have pump out the R-12 disconnect the AC hose, remove radiator, remove condenser, install the shroud, reconnect the AC line, refill with R-12, etc.

The fan cooling system is another joke, three thermoswitches, three relays and probably a couple of temperature sensors that I haven't figured out yet. The old Audi 4000 system was far more reliable! Troubleshooting is next to impossible, the Bentley manual just $#cks, costs a fortune and has lots of useless pictures and diagrams. It seems everything that I try to troubleshoot is not relevant to my model as I have discovered when replacing the heater core and trying to figure out the electrical system for the cooling system. If you follow the manual it actually implies that you have to remove the engine in order to change the timing belt. After replacing some very expensive relays, checking the other relays, thermoswitches and wiring, it should all work but it doesn't. Instead the gauge needle goes up to the first mark after the thick one (normal), then the fan kicks on for 5 seconds goes off and stays off for a much longer time. With a cap of 17-22psi opening all the pressure will do wonderful stuff to your hoses, expansion tank and the plastic parts on the radiator and heater core.

I think that the only solution to the hot running problem is to bypass all the switches and install a manual switch as I often hear. Forget the $$$ Audi piece of cr@p shroud and fabricate a new one from either sheet metal or fiberglass cloth and resin. For the hell of it I jumped the relay for the low speed fan and “voila” the whole system stays cool as a cucumber and the gauge reads what is supposed to be.