She's had a long life, the Impala. It's coming up on half a century now; the years she's been in service. From Sal Moriarty in 1967 to Dean Winchester in the present day, all that time she's been driving dutifully on. And those years have indeed been full of driving: she's never been a car just meant to sit and look pretty on someone's driveway. No, the Impala, good looking though she is, is no showpiece. She's seen more than her fair share of mileage; driven the length and breadth of the United States several times over, perhaps even guzzled up enough gas to drive to the moon and back. And still she keeps going.
Many a car that's seen the years and miles she has would have given out by now; engines and wheels worn to the point of exhaustion and being good for nothing but scrap. But not her. Like her owner, she's no quitter. She's taken some crap over the years; been smashed to pieces and rebuilt almost from scratch; brought back to life after gathering dust in a lonely garage limbo for months; even helped stop an apocalypse or two. But even all that still wasn't enough to break her.
Still her wheels turn faithfully on, because that's how she rewards the man who cares for her. The man who put her back together, piece by piece, after a collision with a freight truck nearly destroyed the both of them. The man who convinced John Winchester to rescue her from the unloving used car dealer in the first place and put her back on the road where she belongs. The man whose memories she holds in her air vents and in her soul.
Because even though Dean Winchester has been let down by many things over the years, the Impala isn't one of them. When everything else in his life has been falling to pieces, she's the one constant thing that he can always rely upon. The familiar scent of her worn leather seats is something he can recall from even further back than he remembers holding baby Sammy in his arms, and the car herself has outlasted even John and Bobby in terms of the years Dean's spent with her. Even though there's plenty of times when she could have easily broken down beyond repair, that still hasn't happened. The car's kept going, ready for whenever Dean needs her again. She waited for him to get back from Hell. She patiently hid away while he was on the run, before returning to help him and Sam defeat Dick Roman. Then she waited again for him to get back from Purgatory.
Countless times she's been there to rush him or Sam or John to the hospital, or to help them escape some threat chasing them, or to get them some place fast when time isn't on their side. And countless times she's been there when he's just needed to hit the road and drive, her speakers blasting rock songs so familiar her cassette player almost knows them by heart. Always, whatever Dean needs from her, she'll give it him.
Because that's what this 1967 Chevy Impala does. Maybe now her wheels don't turn as smoothly as they once did, and her suspension creaks more than it used to, and her steering has grown stiffer over the years, but like Dean, she'll carry on. Because if there's one trait that car can be said to have, it's loyalty, and the thrumming heartbeat of her engine won't stop for good until the day that Dean Winchester's does too.