The real cause of injector rattle?

[Ruan]

So I was right all along - your gauge is talking billy bollocks.

HDis are SO thermally efficient, they struggle to maintain temperature when cruising because they're actually spending the vast majority of the energy actually driving the wheels rather than pissing it into the cooling system like other engines do!

The later EGR cooled HDis don't require the coolant heater, however when you disable the EGR, you remove the recovery of heat into the coolant and therefore they struggle again to warm up/stay warm.