+1 on the expansion tank. Mine split at the seam. This was on my 2001 4.4 X5 at about 110000 miles. It was also a good time to flush the system.

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2007 Suzuki Vinson 500 4X4
2007 Toro 6.5hp
2006 BMW X5 4.4 ltr (his)
2001 BMW X5 4.4 ltr (hers)
1994 Honda XR650L
1984 Honda XR80

"Beer is proof that God loves us and wants us to be happy."
Benjamin Franklin