I've been having this discussion with car friends. I recently bought an ex police car, 2010 Hemi Charger with 78000 miles and an unknown to me at the time, 13,100 engine hours. I was expecting 7000-8000. (I didn't know the trick to get hours to show when I inspected before purchase) Most personal cars might have 4000 hours by the time they hit 100,000 miles. My own cars would have about 3000 hours because I drive longer distances and keep my speed up.
Ford Fleet Services says 1 hour of idle time equals 33 miles of wear and tear. Meaning my Charger has a theoretical 432,000 miles. I think Ford's figure is ridiculous. My cop buddy said it seems like a stat to help sell new service vehicles. His assigned 2015 Explorer is approaching 10,000 hours and has just over 50,000 miles, runs great. Ford claims 8000-10000 hours is about the lifespan of a service vehicle in an urban environment.
I don't have much time behind the wheel yet but this Charger is a good strong runner. It was my friends former assigned car. Supposedly the fastest car in the department comprised of 6.0 Caprices and a 14 and 16 hemi chargers.
Regardless of how worn this engine actually is, it doesn't leak, smoke, or have any valve-train noise. No Hemi Tick. All 16 spark plugs were older but showed little to no signs of oil consumption. It is also one of the 50,000 Hemi's recalled in 2014 for failing timing chains, lots of cars lost motors over this. The recall was never performed... It will be soon. Despite all the idle time, it has lasted.