Woohoo.
After 4 years of cool running temp and webasto constantly running...
I found there is another hidden (above driveshaft UJ and behind chassis) thermostat on all A8s, on some near the radiator and some on the side of the gearbox. It regulates coolant flow to the gearbox. If this thermostat is stuck open it means coolant circulates the whole system from cold and never warms up unless it is hot outside.
It is a common part reference and point of failure across many VAG models.
FEBI 38713
VAG 4E0 121 113
Thermostat, coolant ~ £20
Part has arrived so will fit it on monday.
One thing that does puzzle me is what is the wire clip for - it is hard to get to the thermostat but there is a spring clip on each hose and the wire clip looks redundant.
Last edited by snapdragon; 23rd April 2020 at 08:19 AM.
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