Are you doing the coolant pipes? It's the most hard to reach parts of a 3.0 coolant system. Definitely worth replacing both coolant pipes. Everything else can be changed out when leaks occur. Use OEM pipes too. Others are too small. I used calipers to measure OEM vs aftermarket. I have two sets of aftermarket pipes sitting in my garage. They were parts from kits. The transmission oil cooler was a headache. I had to seal it twice. I used OEM seals too.

Distilled water and good flush. Upgrade the water pump to a metal impeller.

My coolant system refresh.

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'06 X5 3.0i - bought @143,123 miles (12/26/20)