No offence taken. As I said, it was an idea I had come across rather than devised. Your point should not be dismissed out of hand. I understood that the IRD cooling was to stop the oil from getting to thin due to the heat generation in the IRD bearings. Is it therefore possible to 'overcool' the IRD?
The max temp of the engine coolant will be limited by the thermostat on the engine coolant. However, the engine will be pushing against this when working hard, so there is a maximum limit as to when they want the coolant to start cooling down a little quicker. The IRD will follow the same pattern as it’s sharing the water.
As the IRD needs to be the same temp as the engine, and the engine runs farley hot whilst in operation, then I would expect naturally to have to keep the IRD at a similar temp, or minimum temp below the engine temp, say 10 degrees for arguments sack. If this were not complied with, then metal expansion at different rates could cause leaks.
On the video’s I posted for the rover kv6 timing belt change they mention there’s a value that closes to allow the engine to warm up quicker prior to the heater, I think, from memory. Hence the engine, and therefore the IRD, are given priority in warming to optimum working temp, over the cabin heater.
I would have thought the IRD heat would be important, as the oil is 85w90. One figure is starting temp and the other is running temp. “How runny the oil is” rating. Hence there must be some rule of thought with respect to IRD oil and water temp v oil condition.
I'm no expert, but I'd put money on it that LR put coolant through the IRD for a number of reasons. Longer life, better operating conditions for the bits n bobs inside.