In comparison to what? Diesel engines in commercial vehicles are extremely reliable. It certainly could be possible for an electric bus to be more reliable, they certainly have less points of mechanical wear. However, there are a lot of power electronics going into charging their batteries and delivering the battery power to the motors.
Plus they smelled like death and produced gross amounts of black smoke.
The only very selective myth I still hear repeated is that diesel engines are more durable now than they were, which isn’t saying much, and skirts around just how much else can and regularly does go wrong with a diesel-powered vehicle.
Flywheel clutches are an expensive nightmare, and the vibration destroys manifolds, cams and exhausts in short order.
That’s only for the dirtiest diesels that aren’t properly using DPFs or AdBlue (which if you’re seriously considering running school buses in 2022 and not using these, you’re a disgrace). Both of these fail regularly and cost a small fortune to replace.
There’s an entire underground industry dedicated to removing the particulate filters from Diesels to improve fuel economy and reliability (because I guess some people just hate kids, who knows?).
Electric vehicles have been around for well over a decade now, the data is back on them, and on the whole they are astonishingly reliable compared to the ICE vehicles they are replacing. There’s a lot of cables, sure, but they’re flexible and aren’t inherently moving parts.
The old ones "run on physics"
Even with that said (and as detailed above) there are so many other parts to a modern Diesel-powered vehicle that can and regularly do go wrong that they get a pass for because it's not in the engine block. I do wonder if this is because people just assume the vehicles are otherwise identical beyond the engine.
It is true that a lot of parts are in common. But there are a lot of moving parts, susceptible to failure in an ICE not in electric.
I spent a lot of money recently fixing an oil leak and replacing the cam belt on my ICE. Routine maintenance (the leak specifically was not routine but leaks generally are).
My next car will be electric, I hope.
For all our family cars over last 30 years, 90% of repair cost was engine. Those oarts are under temperature, pressure and massive friction.
Windshield was cracked.
Something in the TPMS was messed up.
Brake fluid change (another thing that few people do but should be done)
I didn't pay to fix the blind spot warning system, I want to but the repair costs is more than the car is worth.
US Detroit diesels? lol no.