Right after O'Connell, Jonathan, Evie, Ardeth Bay and the museum guy drive through the swarm of crazy people, they crash the car head-on into a large concrete water basin of some sort. The next morning, they drive the same car to see Winston - except the car is not damaged at all. Gee, they must have a pretty good body shop in Cairo.
If you listen to the audio commentary on the DVD, the director says that he wanted the car to be "steaming across the desert" to show that it was damaged. Due to the mainly British film crew there was no steam coming out of the bonnet of the car, they had to settle for broken sounding noises. Why? here in the UK "steaming across the desert" means (in the words of the director) "hauling ass across the desert" so no steam from the bonnet of the car which would make it look more broken.
Also, didn't they all (except the museum guy) escape down that hole? Wouldn't it of been easier to get a different car rather than risking going back and getting the smashed up one?