Took a longish road trip yesterday - filled up just before starting and then at 515 miles - mostly Interstate with one 20 minute back up and about 30 miles of slower roads. On the Interstate I was running 70+ in hilly country (northeastern PA). After topping off the tank, I calculated my fuel mileage - 30.15 mpg - took on 17+ gallons -but the trip computer was reporting 100 miles to go until empty! suggesting a 20+ gallon total capacity, well beyond the spec. The fuel gauge was low, between the last tick and E but no warning light (is there one?) Is there a calibration function or might I have an optimistic fuel guage?

('03 V70, Michelin MXV4s running at 38psi)

 

21 gal to be exact