As a general efficient-driving guideline published by the DGT in 2016, at what engine speed is an upshift advised for a diesel car in favourable conditions?

Correct answer

Between 1500 and 2000 revolutions per minute.

Approximately 1,500–2,000 rpm in that guideline. It is neither a mandatory rule nor a universal range for all engines and situations. Follow manufacturer guidance and adapt the gear to load, gradient and required response, without forcing an unsuitable engine speed or compromising safety.