I saw a similar thread that was specific to the N52 engine, so let's open it up to the whole crowd. I tried searching but didn't see a similar poll. N52 guys/gals, definitely respond to this poll as well.
N52 thread here:
http://www.e90post.com/forums/showthread.php?t=725313
Many of us are starting to get well into the range where they start to fail, so let's get some statistics.
Feel free to comment if you have a engine power mod, as that could have an effect on the failure rate.
If you had it replaced, feel free to reply with the cost and whether it was dealer or independent shop.
If you replaced it as a preventative measure, feel free to post that too in the thread.
Mine has ~55,000 miles and is on the original pump.
If we end up with a lot of responses, I will try to make some graphs/stats and stuff and post them here at the top. Thanks!
[[[[ Update 6/22/2015 ]]]]
Everyone, I have compiled initial statistics based on 559 responses so far.
This gives the failure probability and the +/- 95% confidence intervals for that failure rate.
Everyone help out by voting!
Also, there will likely be a skew towards more failures given that many people with healthy water pumps may not check out the thread.
For those of you interested in the calculation details, I switched to a binomial-based distribution which is better for proportions:
Plot of estimated failure rate during specific mileage intervals:
Plot of estimated failure rate before a specific mileage (perhaps more interesting to some of us):
(I didn't really propagate the uncertainty correctly, so the uncertainty is probably larger at higher mileages)
Looks like there may be a lot of failures between 60-75,000 miles, and a relative lull in failures between 90-105k miles (though still uncertain). This could mean that some pumps fail early and other batches are more robust. However, it could also be a function of the heterogeneous sample of turbo/non-turbo cars, different driving styles, etc...
Still, predicting a 50% chance of failure before 75,000 miles kind of sucks!
Interesting nonetheless!
Disclaimer, courtesy of a fellow member. This analysis is not meant to encourage people to change there water pumps...
Quote:
Originally Posted by Efthreeoh
Not to throw cold water on this whole statistics lesson, but I think the better data to make a statistical analysis from is time (rather than mileage) and type of use (i.e. percent split between city and hwy driving). The water pump fails due to the heat load it sees based on the environment it operates in. A water pump in car that sees more stop and go driving in Dallas, Texas will fail at a different mileage than a water pump in a car that sees no heavy traffic in Anchorage, Alaska. Tying failure rates to mileage, while you can make a statistical evaluation, is not a true measurement of predictability when a pump will fail as a result of mileage.
Also, throwing in N52s into the data set is going to skew the results because the water pumps for each engine are different parts. You should not be trying to correlate failure rates for two different models of water pumps.
Considering the high cost of replacement, it would be a disservice to members of this Forum to have them use this thread to decide when a preemptive replacement of the water pump should be made (i.e at 70,000 miles). Being that the cost for replacement is anywhere between $800 - $1,200 (non-DIY), it is probably better for an owner to wait until the pump fails and have roadside assistance insurance to handle the tow bill. A much better investment would be for an owner to buy a BMW-reading scan tool and periodically scan the car for the shadow codes that indicate the pump is starting to fail. Having been through this whole ordeal, this is just my opinion.
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