Am I who I was?

Sometimes I get the feeling that I'm not who I was 4 days ago, let alone 4 years ago. Idea's, memories, and personalities, come and go. My ego rises and falls, and what made me Chris years ago, isn't what makes me Chris currently. In essence it's a new Chris, with new idea's, new hobbies, passions, goals etc. Everyone goes through this cycle, its unheard of for someone to not change from childhood to adulthood in the slightest. I feel as though my inner core, the foundation of who I am has been remodeled, a face lift on an old run down store. I love the two following analogies to prove my point. If you have an older car that you wish to get restored. So you get a whole new set of parts for it, new interior, and new engine parts etc... As you applying these new body pieces and engine parts, you get to thinking... At what point is this car not the same car? If you fix it up removing random piece after piece, eventually you'll have a brand new car. So it shouldn't be thought of as the same car should it? Another great idea of this is lets say you have a train of about 40 cars long. On its way across the united states, this train (which is named 9001), makes frequent stops along its route, picking up and dropping off cars at its station stops. Freight comes and goes. By the time it reaches its destination across the country, Mostly all of the cars have been switched and swapped out, even the engine pulling the train has been replaced multiple times with new conductors. When the train finally comes to its final stop, is it still 9001? Technically it shouldn't be considered the same train that left.
These idea's that we're never the same person that wakes up, give me a need to really examine who I was and who I am now. I've seen a lot of my own personality change, and warp, and I have to wonder... Am I who I was?