Fan switch needs proper radiator level to work

[M3 Mitch]

On a lot of VAG cars the radiator fan is controlled by a 2-prong or 3-prong switch on the "cold" side of the radiator and a lot of these radiators are horizontal rather than vertical flow - my fan recently quit working and long story short I was just low on coolant - with the engine off the coolant didn't look *that* low but with the engine running and up to temperature the level on the cold side of the radiator drops quite a bit. In fact it dropped enough to uncover the switch, which of course never turned the fan on, regardless of coolant temp. When I unplugged the wiring from the switch and jumpered the appropriate wires the fan of course ran, which led me to think the switch (recently replaced) had gone bad. However just topping up the radiator fixed the problem.

So, now I have a spare rad switch to put on the shelf - it's not worth returning it.

Hope this saves someone the trouble.

[agent006]

Sister-problem to the headlight washers that stop working when the fluid level is low. Took me fecking ages to work that one out.