Service Stations in Italy often keep to the same hours as shops. Many of them close for approximately 3 hours over the lunch period. On the main roads there are plenty of 24-hour stations with self-service dispensers that accept euro notes and the majority of them also accept major credit cards (although not all of them). It is quite common at the smaller fuel station that an attendant will fill the car for you.
Fill it up please/ Faccia il pieno per favore