Revealing mistake: In the scene where Christie Brinkley takes off her clothes and invites Chevy into the pool, he takes off his pants and we are supposed to assume he's naked. When he dives in you can see he's wearing flesh coloured underwear.
Other mistake: In the first gas station scene, Ellen directs Clark to the gas tank opening which Clark has thus far been unable to locate. Despite being a brand-new car, the inside of the gas tank lid is completely rusted.
Factual error: The whole movie he drives without any valid license plate. Just a crooked colored plate from the auto store. He would have been pulled over for that immediately, and the car probably would be impounded. Then when he does get pulled over for the leash, the cop says nothing about invalid plates. But he asks for registration proof and Clark shows it, even though he has no legal plates. Plus his meaningless plate is crooked, which is also illegal.