Your serpetine belt tensioner has a 17mm hex cast into it - use a socket on it and rotate it so the belt releases - then use a 4 or 5mm allen wrench and insert it between the two halves of the tensioner (its a bit on the lower side) and it will lock the tensioner in service position.

Do not try to undo that torx screw in the tensioner.

to undo the fan you need a big wrench to undo the big nut from the water pump shaft - after the fan is removed you can see the entire water pump and pulley, undo all bolts and remove.

You might want to double check what you have ordered - there are several mutants of this engine and some have an oil cooler on the oil filter mount. Engines with those coolers would have an additional hole in the water pump.

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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)