sounds like they wanted to heat the head evenly and to prevent air pockets. Its a pretty high point in the system, It would become nightmarish trying to purge the trapped air if it did not have such a setup.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)