As over-the-air (OTA) vehicle software and firmware updates become a common and frequent practice, Original Equipment Manufacturers (OEMs) seek ways to reduce costs by utilizing opportunistic free wireless links into the vehicle. Unlike previous works that rely on opportunistic direct wireless links between the vehicle and network infrastructure (or other vehicles), our proposed VehiCache system uses trusted mobile devices, e.g., smart phones, as agents, to bridge between the cloud and the vehicle, and seamlessly convey OTA data into the vehicle, in a secure, and a cost effective manner. VehiCache was simulated and analyzed under both the traditional car-ownership, and the popularity-gaining-car-sharing usage models, showing that VehiCache is capable of distributing non-critical OTA content with high probability within a reasonable amount of time. Finally, preliminary observations from a VehiCache proof-of-concept demonstrator are reported.