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Today I set out to fix what I had diagnosed last week as a leaking windshield reservoir pump. I know this is a common problem on all BMW's. I owned an 2001 4.4L X5 before and it had the same problem. I decided to document the work I did on my 2008 M5 and show some analysis result as to why these pumps actually fail. Remember: Leaks are always bad. Enjoy.

Here is a picture of the reservoir located in the driver side front wheel well, behind the plastic lining near the bumper. You will have to remove the wheel, remove some of the front side liner screws and fold back the liner a bit to get to it. TIS will tell you how. As you can see, there is some blue residue on the tank from the leak near the smaller of the two pumps attached to the reservoir. The larger headlight pump to the left does not leak (in my case). When I was operating the pump, the fluid was exiting through the (obscure) weep hole in the pump housing. Besides that, it would slowly leak when the car was sitting in my garage. Note that the leaking shows up elsewhere under the car as the pump leaks onto the front bottom cover from where it will find the nearest/lowest point weep hole in it. You may conclude initially you have some other kind of leak, but when you catch the fluid you will find it is the typical blue windshield wiper fluid.
<a href="" target="_blank"><img src="" border="0" alt=" photo M5_WSW_reservoir_0.jpg"/></a>

Step one is to disconnect the hose and drain the reservoir. If you do it outside, you can proceed and lift the pump out of the grommet/filter installed in the reservoir. (It will flow away via the bottom cover weep holes.) It slides up and comes out. Disconnect it from the wire harness by unlatching the connector by its small tab.
<a href="" target="_blank"><img src="" border="0" alt=" photo M5_WSW_reservoir_1.jpg"/></a>

This grommet is often blamed for this leak by the dealer. On my X5 they were suspect so I replaced it here as well, but I am pretty sure it was not the cause of the leak in this case. The grommet I took out fell apart, the filter piece of it stayed in the reservoir and I had to pry it out. The right grommet is the old one, the left one is the new one. Clearly a design change to keep it together better.
<a href="" target="_blank"><img src="" border="0" alt=" photo M5_WSW_reservoir_2.jpg"/></a>

In the picture below, the grey pump is the old pump and the right black pump is the new version. Definitely a different design and OEM supplier. It does not look broken, but it definitely is! More about this below. The weep hole on the grey pump is the square section on the black part. From there the fluid escapes when the pump is operated.
<a href="" target="_blank"><img src="" border="0" alt=" photo M5_WSW_reservoir_3.jpg"/></a>

The failure can be seen in the next picture below. I took the pump apart and it shows fluid in the 'dry side' of the pump. The motor axle has a rubber black grommet that is the culprit. It is a poor seal design. After a while, the motor's axle rotation causes the seal to wear and fluid will slowly seep through. When the motor is operated, the increased pressure forces a lot of fluid through this leaking seal. It comes out of the weep hole of the motor at a good clip! The really bad part is that it gets into the e-motor, through its front bearing. Failure of the motor is imminent.
<a href="" target="_blank"><img src="" border="0" alt=" photo M5_WSW_reservoir_4.jpg"/></a>

For some reason I still had the two old pumps of my X5 laying around and opened these up as well. It basically reconfirms what I explained above. The failed pump is in a really bad state as you can see. It had been going on for a while as I was slow to address it. This is yet another design, albeit that it could be fitted into the M5.
<a href="" target="_blank"><img src="" border="0" alt=" photo M5_WSW_reservoir_6.jpg"/></a>

I also replaced the hose attachement elbow that is pushed on the pump's exit tube. I had a few laying around so, just to be as thorough as possible, I renewed this as well. I do not want to do this again, but given that BMW has not gotten the design right, at least between 2001 and 2008, I may have to do it again in a few years. Oh well.
<a href="" target="_blank"><img src="" border="0" alt=" photo M5_WSW_reservoir_9.jpg"/></a>

Anyway, I put the new filter/grommet back in the tank and placed the new motor onto the tank. You will have to press the spout of the pump into the grommet. Be careful not to damage the grommet. Push it in straight down; no angling it in. Do not take it out and put it back in a few times as it may damage the rubber and cause a subsequent (new) leak. Reconnect the harness. Before I buttoned everything up, I filled the tank and checked for leaks. As expected, no more issues. And I gave the tank a quick cleaning. Good to go.
<a href="" target="_blank"><img src="" border="0" alt=" photo M5_WSW_reservoir_5.jpg"/></a>

I really hope BMW has addressed this by now on the newer beemers, but my gut says it is still the same old solution. Ha! :grinyes:
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