Ensure that the engine is cold. Lift the front of the car with a floor jack and lower it onto a pair of jack stands. Turn the heater controller (or press the buttons if electronically controlled) to hot and turn the ignition key to the "On" position.
Place a container under the passenger side of the engine under the manifold. Loosen and remove the coolant drain plug, located in the block just below the manifold. Drain all of the coolant from the engine. Install and tighten the drain plug with a new sealing ring to 18 foot-pounds.
Move the coolant container under the radiator. Loosen and remove the plastic drain plug at the bottom of the radiator and drain the coolant. Reinstall the drain plug and tighten it to 2.2 foot-pounds. Do not over-tighten it.
Pry the cap off of the belt tensioner. Loosen the belt tensioner for the poly-ribbed belts with a socket or the appropriately sized Allen wrench. This may turn in either direction, depending on the type of tensioner, so loosen it in both directions to see how it loosens. Slide the belts around the fan, nearby components and out of the engine.
Remove the small plastic rivets that hold the fan frame to the radiator by prying them up and out very carefully with a screwdriver. Disconnect the coolant reservoir hose where it goes to the engine near the water pump. Disconnect the coolant overflow hose. Remove the fan, fan frame and coolant reservoir at the same time.
Remove the four small nuts that hold the fan pulley to the water pump with a socket and ratchet. Loosen and remove the four bolts that hold the water pump to the engine. Remove the water pump from the engine bay. Tap it lightly with a hammer if needed.
Clean the bore in the engine where the water pump installs so there is no debris. Clean it with a wire brush as well. Install the new water pump with a new O-ring. Place a layer of white lithium grease on the O-ring to ensure a good seal. Install the water pump and tighten the bolts to 8 foot-pounds. Bolt the fan pulley onto the new water pump.
Reinstall the fan, fan frame and coolant reservoir. Reinstall the plastic rivets that hold the fan frame to the radiator. Reinstall the belts. Tighten the belt tensioner.
Remove the small plastic bleed screw located to the right of the radiator cap. Place a funnel in the expansion tank and fill the cooling system very slowly with new coolant. Use 10 quarts for the 325. Continue filling until coolant comes out of the bleed screw. Fill until there are no air bubbles coming out with the coolant. Wipe up spilled coolant. Tighten the bleed screw to 71 foot-pounds. Run the engine and top up the coolant if necessary.The 1992 BMW 325i is part of the E36 generation of the strong-selling 3 Series. The E36 325i offers strong performance and a thrilling driving experience that most BMWs deliver. One weak spot on many E36s (and many BMWs, for that matter) is the cooling system. Radiators, water pumps and thermostats have all been known to fail. Replacing the water pump on an E36 is pretty easy with the right tools.