Travelling by car
The motor fuel in the tank of your car is duty-free. When entering Austria, you may bring another 10 liters duty-free in a jerry can.
Travellers with EU domicile can re-import their car duty-free after repairs abroad, if they can prove that an unexpected damage occurred that prevented further travelling. Only those repairs may be made that are absolutely necessary for continuing the journey.
Whenever additional repairs are made, you must hand in a customs declaration upon entry into Austria and pay the import charges due on the prices of the repairs. Whenever a damage occurred prior to leaving the country, or when the work done covers more than the repairs (fitting a spoiler, getting a new paint coat), you should submit a customs declaration in any event, when re-entering the EU, as you may possibly have to pay import charges on the entire car otherwise.
Whenever you import components for your car duty-free, as part of your allowance of € 300, make sure to bring them with you as separate items that have not yet been fitted or assembled (e.g. tires, radio). This is the only way that these components can be treated as self-contained goods.
When using a foreign rented car you may travel back to the EU country where you are domiciled, but must not, for example, take it on an excursion to another EU country. There is one exemption regarding Switzerland: a rented car registered in Switzerland may be used for private purposes in the EU for a period of eight days (calculated as of the date when the car is hired from the Swiss rental company). You must, however, re-export the car or hand it back to a car rental company in the EU before this period has expired.
Travellers not domiciled in the EU may use their car duty-free for private purposes in the EU for a maximum period of six months. Passenger cars must then be re-exported in an unchanged condition. Apart from a few exceptions, you may neither rent, lease or otherwise dispose of the vehicle, nor have any re-fittings made that exceed repairs. You will need a permit by the customs point for any major changes.