quattroworld

Under the tank, next to the coolant level sensor, there's a hose that connects to a hole that routes through the tank and into the space between the cap and the tank.

I imagine this is there so that when the cap's spring is opened by an overpressure situation, the resulting slurry of coolant and steam is routed down into the bottom of the engine compartment instead of all over the engine compartment and possibly the shlub who opened the hood to see what the fuss was about.

The hose -- does it route between the engine and the heat shield or between the heat shield and the inner fender?

The attached picture is of the coolant tank from the side -- the overflow hose is the thing directly below the tank with the little foil collar.

(BTW -- non-oem tanks don't have the plastic fitting that attaches between the tank and this hose; the OEM has the foil collar and the barb fitting but not the overflow hose itself)