Yes, we know it's on the radio and not TV, but Car Talk at its peak had a weekly audience of 3.3 million listeners.
Britain might lead the way when it comes to automotive television, but the US produced an automotive radio show which would become a runaway hit, even with people who don't especially care about cars. If such records existed, the hosts would also surely hold the record for the thickest Boston accents in existence, and it is very likely that linguists will study it in the future. Still, their knowledge of cars cannot be denied, to an extent which is occasionally truly startling.
The show (yes, we're fully aware it's not on TV) is hosted by brothers Tom and Ray Magliozzi, who also refer to themselves as "Click and Clack" or "The Tappet Brothers". Both brothers hold degrees from MIT (and Tom has a PhD from Boston University), and worked for a number of years in unrelated fields before deciding to open a garage together. At first, this shop would simply rent space and tools to people who wished to fix their own cars. This proved unprofitable, and the garage was eventually converted into a more traditional setup, and indeed the brothers still operate such a garage.
They got their start on radio after opening the original garage, when they were asked to be part of a panel of automotive experts on a local radio show from Boston's WBUR. Quite coincidentally, this was in 1977, the same year that Top Gear launched as a local automotive TV show in Birmingham in the UK. But Car Talk stayed as a local show for much longer, and it wasn't until 1987 when the show was picked up nationally by NPR. The format was simple enough, especially at first. People with car problems or questions would call in and have their questions answered on the air.
In the early years, these tended to be strictly technical questions, and it's not so difficult to see why a show about spark plug gaps took a while to go national. What would ultimately broaden the appeal of the show and allow it to attract a bigger audience was the humor which the two brothers brought to the show. And although in many cases these are simply the same jokes told over and over, any amount of humor can make a big difference in what would otherwise be a terribly dry show. More recent additions included a segment they call "Stump the Chumps" wherein callers they had given advice to in earlier shows are called back and asked whether the advice had been at all helpful.
As a way to lend the brothers' automotive expertise more credibility, it's really quite a good idea, especially when predictions concerning lesser-known or more difficult to diagnose problems prove correct.
Later shows include the addition of a puzzle segment which is rarely car-related at all. Indeed, at times, large parts of the show are only loosely connected to cars, if at all. And indeed, toward the end, there were bigger segments devoted to the discussion of environmental concerns. But NPR was always a sort of an odd venue for an automotive repair show anyway, so the fact that it was a sort of an offbeat one is less surprising than the fact that it existed at all. And of course, a large percentage of the NPR listing audience seemed uncomfortable even talking about automotive repair without also bringing up the environment.
You can mock this if you wish, but with a listening audience of 3.3 million at the show's height, Car Talk was by far the most popular radio show of its kind ever. The Magliozzi brothers have retired from radio as of October. But the show will remain on the air, and the producers will simply be playing previously recorded but unaired segments for some time. In fact, they estimate that they have about 8 years' worth of material to get through before they need to start repeating.