I changed the AT thermostat on both the X3 and X5 today. Both the expansion tanks cracked within a few weeks of each other but I never replaced the AT thermostat when I changed the tank. Weird how both tanks cracked almost at the same time and both AT thermostats failed?

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E90 318i 2007 N46 2.0 Manual
E53 X5 2004 M54 3.0 Sport Auto
E83 X3 2004 M54 2.5 Auto