Factual error: When the car goes to the bottom of the ocean after the chase, the water in it is raising as if leaking in, despite the fact that the door on Hiro's side is missing and the water should be rushing in. (00:50:15)
Suggested correction: I watched the scene and it looks like it's filling up the way it should. It's looks similar to the way a car fills up after being submerged with the windows open.
Not true, water is still filling up the car way too slow for an opening like this. The car should be filled up immediately.
You're wrong thinking it would fill up immediately. But even so, it fills up in about 10 seconds (even less if the shot of it filling up is meant to be a simultaneous shot and not continuous).