The real cause of injector rattle?

[JTaylor2005]

Thing is, diesel engines are SO thermally efficient because of the fact normally they are running in an excess of air and have high compression ratios... The temperature of the coolant is nowhere near as important as it is in a spark ignition engine. The classic rule "hotter = more efficient" doesn't stand true from what I've seen, I'd say there's very much a "sweet spot", but I don't think it'd make near any discernible difference in economy, rather just f*ck up stuff like the viscosity of oil - you're looking at the water temperature purely from a efficiency point of view.

There are FAR greater factors affecting the efficiency of DI diesels rather than coolant temperature, notably commencement of injection angle, which is closely intertwined with emissions. I would agree they need to get up to temperature, however this is more from a lubrication point of view, rather a thermal dynamics point of view. Remember in a DI diesel, the part that contains the combustion and where a lot of the heat will go is the piston... The water cooling system is under very little load, the vast majority of the thermal energy is coming from the oil, since this is what cools the pistons.

Have you ever seen a DI diesel melt a cylinder head before a piston....

Of course, this is my opinion on the matter. Very happy to have a debate.

That all sounds very true and reasonable. I have always been under the impression that coolant temperature has a large effect on the actual cylinder wall temperatures. Which would then have an effect on fuel atomization etc rather than it condensing against a cold cylinder wall. But that could be total crap and tbh I would expect it would have to be a large difference in temperature to make a noticable difference.

However thinking of that it would be likely that would be more of an indirect injection system where the head has to be hot to help keep the diesel mist finer rather than on a setup where your injecting at 300 bar through micron sized holes.