3D graphical functions in cars enjoy growing popularity. For instance, analog instruments of the instrument cluster are replaced by digital 3D displays as shown by Mercedes-Benz in the F125 prototype car. The trend to use 3D applications expands into two directions: towards more safety-relevant applications such as the speedometer and towards third-party applications, e.g., from an app store. In order to save cost, energy, and installation space, all these applications should share a single GPU. GPU sharing brings up the problem of providing real-time guarantees for rendering content of time-sensitive applications like the speedometer. To solve this problem, we present a real-time GPU scheduling framework which provides strong guarantees for critical applications while still giving as much GPU resources to less important applications as possible, thus ensuring a high GPU utilization. Since current GPUs are not preemptible, we use the estimated execution time of each GPU rendering job to make the scheduling decisions. Our evaluations show that our scheduler guarantees given real-time constraints, while achieving a high GPU utilization of 97%. Moreover, scheduling is performed highly efficient in real-time with less than 10 us latency.