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systems have been known for being troublesome for quite some time. One
of the principle areas of failure are the thermostat and water pump.
Some of the old style water pumps had a plastic impeller that has a tendency
to become brittle and break off after many years of service. BMW has
replaced the plastic impeller in recent years with a metal one. If you
know that you have a plastic impeller in your car, then you should replace
it as soon as possible. Overheating problems are common on these cars,
and if your engine overheats, you may find yourself having to replace your
head gasket, which is not cheap.
Begin the process by
gaining access to your water pump. This requires the removal of the
fan and belts, as well as the removal of all coolant from the system.
See the following technical articles for instructions on how to get to this
With all of your
equipment removed, the front of your engine should resemble
Figure 1. Remove the fan pulley from the water pump - it is held
on with four small nuts. Your water pump should now resemble
2. Loosen the four nuts that hold the water pump to the engine
block. Then, using a rubber mallet, softly tap on the side of the
water pump (Figure
3). It should separate from the block after a few taps with the
rubber mallet (Figure
4). Once the water pump is loose, you should be able to pull it
out of the engine block.
shows a brand new water pump with the metal impeller.
and Figure 8
show the differences between the plastic one and the metal one. There
is no functional difference - they will both pump the same amount of coolant
through the system.
With the pump removed, check the inside bore where the water pump fits for
debris or corrosion (Figure
With a wire brush, remove any corrosion or debris that may have built up
10). Install the new water pump using a new o-ring. Place a
little bit of white lithium grease around the o-ring to ensure that you have
a good seal, and to ease installation of the pump into the engine block (Figure
11). Install the new pump and tighten down the four bolts that
attach it to the block. Torque them to 8 ft-lbs - no tighter.
shows your new water pump installed. Reattach the fan pulley, the fan,
and all of your belts. Refill and bleed the system, and you should be
good to go! While replacing your water pump, it's also a good time to
replace your thermostat, while you're in there.
Well, there you have it - it's
really not too difficult at all. If you would like to see
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