Nerdist, writing after a 2015 set visit with the show's picture car coordinator, Jeff Budnick, called the hero car one of eight; the count is the writer's, not a quote from Budnick. By Nerdist's account the hero car was in almost every shot of the car and used almost every day, and had 12,000 miles when the production bought it and about 15,000 by late 2015. TV Insider reports that Ackles once said the hero car started life baby blue, with a matching interior.511
TV Insider later counted nine over 15 seasons: one main hero car, a couple of backups, a cutaway car for tight camera angles, cars for parts and several stunt cars. It does not say who counted (see the ruling).5one source
Budnick watched online auction sites for backup and parts cars and drove one back from Nebraska to Vancouver. He said four-door 1967 Impalas had once been «five hundred dollar cars» nobody wanted, that owners now wanted «five thousand and up» because of the show, and that he kept a warehouse of Impala parts and cars.11one source
In the season 1 finale, «Devil's Trap» (The WB, 4 May 2006), a semi-trailer truck rams the car. For the crash the car and the truck were cabled together with a winch and driven at each other; the car stuck in the truck's bumper. The production kept its wrecks, and the season 1 car shows up in the background of season 11's third episode.1112
Wikipedia describes a rig called «Highways» for side views of the car: LED lights carried past it made it look as if it were moving.6one source
For the episode «Baby», Extra, which visited the set, reported that eight cars were used. Cameras were rigged in the cars, the sound man rode in the trunk, and Ackles and Padalecki drove off with no crew.8one source