Yes and yes. Keep in mind tho that drowning is not recommended way to go. Painful, stress inducing and with unpleasantly high chance of being rescued.
EDIT - by answering "yes" to the first question i mean that drowning in general is a valid way to go if undisturbed, especially if you encase yourself in metal car coffin but since car floats for a while there's strong chance that either SI kicks in or someone sees your "accident" and rushes to the rescue.