Audi 80 2.6 quattro 20L Consumption far too high

Hello, I bought an Audi 80 2.6 quattro a few days ago and I am satisfied, would not be the consumption of 20-25L in normal driving mode! I now have 30€ so about 30L and after 150km the tank needle was again in the reserve… that can’t be normal, I inquired in front of it in the inet and there it is 10-12L with fast driving 15-17… moreover it is not really warm according to the temperature indicator so 70 degrees! Think that’s the thermostat because I had the same thing with me inem s3 8l already. But can that be the reason for a double consumption? Ask for a helpful answer. 216 000 km switch Limo Bj 93 Stefan