Quote:
Originally Posted by Lucky1
On traditional mechanical water pumps I always hear the rule of thumb of replace around 100,000km or 62,500 miles or when replacing timing belt. So in that respect we've got our money's worth. Its just that BMW does not endorse this and ignores the electric driven water pump replacement as a scheduled maintenance item. I guess the reality is it doesn't last forever its just a little less known what the MTBF is on the N52 (probably a wide deviance between cars and environmental conditions). The N54/N55 seems to suffer more frequent early failures I've heard cited from the additional heat the pump is exposed to but it too is still hard to predict from a timing perspective I'm inferring.
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I'd like to chime in on this since I've owned BMWs for 30 years and currently have, or had all three types of BMW waterpumps discussed above. Further my N52 in my E90 has 358,000 miles on it and 7 years ago I was the one who discovered the N52 shows waterpump trouble codes when scanned with a BMW scan tool. In general most manufacturers do not call for a periodic water pump replacement as preventative maintenance.
There are basically 3 types of driven water pumps used in BMWs. (1) Electric, (2) belt-driven from the engine accessory (serpentine) drive belt, and (3) belt-driven off the camshaft timing belt. The only modern BMW engine that used a camshaft belt-driven water pump was the M20 straight-6 found in the 3 and 5 series cars of the late 1970's through the early 1990's. Japanese cars have used a cam belt driven pump as a common design until recently. The periodic replacement spec for cam driven pumps is tied to cam belt changes simply for convenience and time saving while having the cam belt cover off and the belt off, the pump is easily changed. If the pump were to fail later, all the work (and cost) to replace the cam belt would be lost. The replacement spec has nothing to do with the robustness of the pump assembly itself. And really, only cam belt-driven waterpump engines have a periodic water pump replacement recommendation from the manufacturer related to the cam belt replacement requirement.
Engine accessory belt-driven water pumps are the most common design used. Most manufactures do not have a recommended replacement interval for this design. Most all belt-driven pumps of this type have a weep hole built into the pump case. The hole is there to provide a visual and olfactory signal for an impending pump failure. The weep hole design allows for a small amount of coolant to leak from the pump when the water pump shaft seal begins to leak due to wear. Once the seal begins to leak, the bearing behind the seal gets wet and eventually fails. The weep hole allows the coolant to leak with the coolant smell a tell tale sign the pump is near failure. Because these type of belt driven water pumps have this built-in failure warning, they normally do not have a periodic replacement recommendation. BMW M42 and M44 engines are notorious for failing water pumps, but due to a plastic impeller used for the original design.
The N52 electric pumps primarily fail due to heat cycling. The control electronics are packaged into the end of the pump case and get very hot. Over time the electronics fail from being over-heated and the pump begins to vary in speed, eventually stopping to turn altogether. There are trouble codes that indicate the pump is starting to fail, but unless the car is scanned with a BMW scan tool, the owner will never know the pump is failing. Worse, in the E90 there is no coolant temp gauge, so you can't see the engine is overheating (unlike the OP's wife did). So, in the E90, the engine overheats and the only indication is a yellow over-heating symbol with a immediate red over-temp warning. IMO it's a poor design for two reasons, (a) the electronics are in a intolerable environment; BMW should have remote-mounted the pump control electronics for better heat dissipation; and (b) there should be a better indication of pump failure for those cars without temperature gauges. Review the E90 Forum and the consensus is the water pumps last about 100,000 miles, but it's really environmentally based on how and where the car is driven. Mine failed at 149,000 miles on a 100 deg. F day in July. A few have gone over 200,000 miles. My Z4 N52 at 10 years and 90,000 miles has yet to show a failure code. The E90 pump is tightly packaged and the end of the pump with the electronics sits just a few inches away from the radiator and under the exhaust manifold. The Z4's engine compartment is a bit more open, which may allow the pump to stay cooler.
The N54/N55 electric pumps can fail due to the electronics over heating and because in someone's wisdom, the N54 pump uses a plastic impeller case, which cracks and leaks; another stupid design choice. The N52 pump uses an aluminum impeller case. The two pumps are not interchangeable; the N52 is a 200-watt pump and the N54 pump is 400-watts. BMW doesn't recommend a preventative maintenance replacement schedule because the pump, in theory, shouldn't fail. I'd bet outside of Forum sightings, most pumps do not fail within the life span of the original owner. MTBF calculations being what they are, it's obvious that the longer the pump is in service, the more likely it is to fail, which is the case with any machine or electronic device.
My 2 cents.
As a side note... My 2008 Z4 3.0si Coupe, which I bought used at 23,000 miles in December 2014 (now has 92K), had a cupholder break, has a noisy throwout bearing (had it when I bought it), and the little tab that closes the switch for the storage cubby light was broken (I fixed it with a small wood screw). I have the sports seats, and the driver's backrest squeaks on and off; I've not yet pulled the seat to diagnose it. Lastly, I had to replace the left HID bulb a few years ago, it was periodically failing. Not a bad service record for a BMW IMO.