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BMW cooling systems are known for being troublesome. The thermostat and
water pump are two of the principle areas of failure. Some of the old-style
water pumps have a plastic impeller that becomes brittle and breaks off
after many years of service. BMW has replaced the plastic impeller in recent
years with a metal one. If you know you have a plastic impeller in your car,
replace it as soon as possible. Overheating problems are common on these
cars, and if your engine overheats, you may find yourself replacing the head
gasket, which is not cheap (see our head gasket replacement article).
Begin by gaining access to
the water pump. Remove the fan and belts (Projects 5 and 34), and remove all
coolant from the system (Project 33).
With your equipment
removed, the front part of the engine should be very accessible. Remove the
fan pulley from the water pump; it is held on with four small nuts (see
Project 34). Loosen the four nuts that hold the water pump to the engine
block. Then, using a rubber mallet, softly tap the side of the water pump.
It should separate from the block after a few taps. Once the water pump is
loose, pull it out of the engine block.
With the pump removed,
check the inside bore (where the water pump fits) for debris or corrosion.
Use a wire brush to remove any corrosion or debris that may have built up
there. Install the new water pump using a new O-ring. Place a bit of white
lithium grease around the O-ring to ensure a good seal and to ease
installation of the pump into the engine block. Insert the new pump, and
tighten the four bolts that attach it to the block. Torque them to 11 N-m (8
ft-lbs) but no tighter.
At this time, I recommend
that you remove the thermostat housing (located above the water pump) and
replace the thermostat as well. The thermostat is a relatively cheap part
that fails easily and can cause your engine to overheat.
This project details water
pump and thermostat replacement on E36 engines. For information on E30 water
pump replacement, please see the 101projects.com website.
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