How to replace an E36 6-cylinder waterpump
From '92 to early '97 BMW installed waterpumps with orange plastic impellers in all of their 6-cylinder motors. The orange plastic they used becomes brittle and cracks apart after as little as 30k miles so I'd recommend swapping out the original pump ASAP. There's no way to tell if the pump has the plastic impeller without removing it from the engine, so if you're not 110% sure that the stock pump has already been replaced, just change it. Those plastic impeller will break apart with absolutely no warning, no noise, nothing. You'll be driving along and all the sudden your temp gauge will be in the red. When your engine overheats you risk damage to your radiator, damage to your engine and a possible accident due to coolant loss. Trust me, it's definitely better to swap your waterpump BEFORE it blows up.

No, I don't have any pics to go along with this write up. I've had people try to take pictures, but they all came out blury because I'm so hella-fast at swapping these out ;) Here's the quick way to do it (takes me ~35 minutes total). If you've overheated your engine due to the waterpump impeller blowing up then you should also install a new thermostat as they tend to stick closed after they've been "cooked".

You'll need the following parts/tools:
- Phillip screwdriver
- Small flat blade screwdriver
- 3/8" drive rachet
- 3/8" drive breaker bar
- 32mm wrench
- Fan clutch removal tool or a BIG flat head screwdriver
- 10mm socket
- 15mm socket, 16mm Socket or 8mm allen socket
- Two M6 sized bolts ~3" long from any hardware store
- BMW Waterpump - #11-51-7-527-799

1) using the phillip screwdriver remove the cover that ducts air to the back of the alternator, 4 metal screws and 2 platic screws.
2) Use the 32mm wrench and either a big screwdriver or the fan removal tool to remove the fan. Spin the nut CLOCKWISE to remove while keeping the waterpump pulley from spinning using the screwdriver or the fan tool. Pull the complete fan out by bending the fan shroud out of the way slightly.
3) Loosen the waterpump pulley bolts with the 10mm socket.
4) Pop off the cover on the belt tensioner with the small flat blade screwdriver, use a socket (15mm, 16mm or 8mm allen depending on model/year) and a breaker bar to turn the tensioner pulley bolt clockwise, slip the belt off of the pulleys.
5) Remove the waterpump pulley bolts, remove the waterpump pulley, remove the waterpump nuts.
6) Thread in M6 bolts in to the threaded lugs on the sides of the old waterpump. Tighten the bolts, they will push the old pump out of the block. Pitch the old pump. Note: if the impeller is shattered, pull all the old pieces out of the block.
7) Lube the o-ring seal on the new waterpump with new coolant, install new pump in block, install and tighten nuts. Install waterpump pulley, install pulley bolts, detension belt tensioner (clockwise) and reinstall belt. The tensioner is spring loaded and will there is no adjustment. Tighen the waterpump pulley bolts and replace cover over belt tensoner pulley.
8) Reinstall fan and tighten.
9) Replace top cover / alt duct.
10) It really helps to have a friend lend a hand by sitting in the car revving the motor and keeping an eye on the temp gauge. Start off by removing the coolant reservoir cap and the plastic bleeder screw right next to it. Fill the coolant reservoir with a 50/50 mix of coolant and distilled water. Have your friend start the car, turn on the heater to full hot on the vent position and rev the motor to about 2500 RPM, if the temp gauge goes past the 12 o'clock position, shut the motor off, let it cool down and start over again. Watch the coolant reservoir, as the engine warms up the coolant level should drop, refill as the coolant is sucked out of the reservoir. Watch the bleeder screw hole also, when coolant with no air bubbles begins to overflow then you're almost done. It's a good idea to have some paper towels handy to mop up any overflow. Screw the bleeder screw back in (be careful to not break the plastic screw) and continue to rev the motor, you should see a continuous stream of coolant spraying in to the reservoir from the small hole at the top. Continue letting that spray in to the reservoir while your friend revs the motor for a couple of minutes, until the gauge hits the 12 o'clock mark, to ensure any remaining air is gone. If the heater is blowing hot air when you're revving the motor AND when the engine is at idle then your cooling system is properly bled. If your vents are blowing cool air at idle then you still have air in the system, try revving the motor more and/or squeeze the radiator hoses to help dislodge any trapped air. Once your system is fully bled, top off the reservoir and replace the cap. Check the coolant level in a day or two and top off as needed.