I need advice dealing with a work problem.

I drive a company car. For some reason, I'm the one who gets to play "musical cars" and they are constantly switching which car I drive. Monday my boss tells me - surprise! You are giving your car to the new person starting today and taking this old car that we are going to trade in in a few months. Tuesday he takes the "old" car and decides there is something wrong with the alignment. He takes it to his special mechanic he loves, hands me the keys to his car and says he'll call me when I need to pick him up.

Fast forward 15 minutes and he's back already. He says the mechanic didn't have time to look at it today but he made an appointment for tomorrow (which is now today). He takes his keys back and gives me my keys. End of conversation.

My boss doesn't show up to work today at all. No emails, no communication, nothing on the calendar. So....was I supposed to take this car to the mechanic? My boss has a history of being a HORRIBLE communicator. What do I say if he shows up tomorrow and asks what the mechanic said about the car? HALP!