I second the "Don't ever go to Walmart" line of thought. Remember - these are the guys who couldn't get food handler licenses.

Your story is only one of many Wal-Mart horror stories that I've heard. My favorite is when they forget to put the drain plug back in.

You'll have a hard time proving that Wal-Mart overfilled it. Especially after you drain it. If you complain enough, you might get your money back but I don't know if you'll get much else. You should attempt to document as much of it as possible - the overfilling of your car, that is. Also, make sure anytime you talk to anyone that you get a full name and what department they're in. And take notes about your conversation, too.

I'd recommend checking how much your local Honda dealership would charge - I got mine changed for $30 bucks.