OK..here is how you really change the water pump on a Z4....(E85, m54 motor, mine is a 2.5) I have done this procedure, and all you will need are one water pump with o-ring, two m6x25mm bolts, a gallon of anti-freeze, simple hand tools, a few blocks of wood, a rolling floor jack, and jack stands. It is a good time to replace the belts, so get both of them. Yes, you do have to move the engine..a little.
1. Jack up the car on one side, place a smaller jackstand under the car where the front stabalizer is bolted to the frame. You just need to get the car up enough to remove the front plastic splashpan. Now remove the splashpan, grip it firmly, and toss it at the nearest BMW engineer to show your gratitude for designing a car that has a sheet metal support with webing placed directly infront of the water pump, thereby making it necessary to move the engine in order to remove the water pump, even though there is enough room infront of the sheet metal support to be able to desing it with a slight 1" dip towards the front of the car thereby providing enough clearance to simply remove the water pump unimpeded. Now, jack up the car a little higher, and remove your small jackstand and place a big jackstand (now that you have the clearance) under the car. place the jack on the other side, and jack it up enough to place another large jackstand under the car at the point where the anti-sway bar (stabilizer) bolts to the frame. Now place a rolling floorjack under the engine and place a block of wood between the jack and the oilpan at the front of the engine. Make sure this block of wood is long enough to support the load across the entire width of the oilpan, in order to srpead the weight of the engine across as much of the oilpan as possible, for obvious reasons. You just need to jack it up to meet the oilpan, don't go any higher yet. The reason you do this now is because the underside of the engine will soon become wet with anti-freeze, making everything slippery.
2. Now remove the belt for the A/C compressor (torx bit needed for tensioner)
3. Remove the top plastic (fanshroud?) cover and loosen but don't remove the bolts on the water pump pulley. Remove the serpentine belt. 16mm socket for the tensioner.
4. Now remove the 10mm bolts on the water pump pulley. Tap the pulley gently to get it off. It is made of plastic, so be careful. Remove the 10mm nuts on the water pump. Now install your m6x25mm bolts into the threaded holes on the water pump. Tighten them, and this will remove the water pump from the engine block. The coolant will spill out, but it won't be a lot. Now remove the upper radiator hose only where it connects to the engine by prying the metal clip. Push it up out of the way against the oil filter housing. You can remove the hose before removing the pump, but I did not because it would otherwise make everything wet that I still have to work on.
5. Now remove the nut at the left engine mount. I think it is a 16mm, might have been 15mm.
6. Jack up the engine slowly, but only go up to the point where the engine mounting bolt is just at the lip of the engine mount, where it almost clears the engine mount, but no further. (I would not want to have to line that thing up upon installation. Besides, it is not necessary to go that far.) You should now be able to pull out the water pump going in the direction of the passenger side.
Ta Da! You've now saved your self a lot of money. Now install the new water pump by lubricating the new o-ring with a little ant-freeze on your hand, and install the water pump. Put the car back together. Pour in some anti-freeze. With the car and the heater running, bleed the air out of the cooling system. (With the bleeder screw located next to the resevior cap.) But keep the old water pump. You will need this during your next trip to Germany, when you get the opportunity to throw it at the head of a BMW z4 engineer. This will make them think! It would be different if these water pumps did not fail prematurely.
Hope this helps!
