It's real - It's the summer Saturday HST▸ from Bristol. Layover of 5 hours.
It has to idle - at least one engine - if the coolant cools below a certain temperature, the engines won't restart & there's no landside power to enable the heaters on the train to heat the coolant.
If you were checking out the train situation before purchasing, you wouldn't see any diesel engines at that location, only electrics, so no smell to be wary of. I do think GWR▸ need to sort this one out.
I find it very surprising that engines can not be shut down when not required.
I remember a spare HST being stabled on the West Somerset Railway, it was certainly not left running continually, and
AFAIK▸ it started OK when called upon. It may well have been periodically started, run for a while until warmed up, and then shut down, by either WSR or
FGW▸ staff, but it was certainly not started every 5 hours ! I doubt that the WSR have a suitable shore supply.
I can see the merit of leaving engines running in exceptionally cold conditions, or if some defect means that re-starting is doubtful, but not routinely.
If a modern* engine wont reliably start after being shut down for 24 hours, let alone 5 hours, then that suggests to me that either the engine or the starter batteries are in poor condition and require attention.
*Yes I know that the HSTs are decades old, but the
MTU▸ engines are relatively new and are a proven design.