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First of all electric water pumps are an excellent idea.
Why?
Because when you are sitting in Atlanta traffic moving at a brisk 5 mph in the summer air on the coolant on a mechanically driven pump isn't circulating fast enough. The electric can and does move the coolant and helps to keep it cooler with fewer spikes. Same thing when cold the thermostat and water pump don't move much coolant allowing the engine and heater core to warm up fast.
This is the future and very likely other manufacturers will follow suit.
BMW water pumps in the 3 series since 1992 (6 cylinder engines) have had mechanical failures and right at the time/ mileage ours do. They started with metal, then phenolic, then metal again and now again phenolic impellers. This is something the Germans have done a poor job of sourcing.
The electric pumps I have seen have failed for a couple of reasons. One is electrical, anyone here drive in salt conditions? Just take a look at one in that part of the country and see the wiring is exposed to the elements even with the pan in place. The other is the phenolic housing which suffers cracks most likely from thermal cycles and just flat out fails.
The idea is excellent the supplier of the pumps, typcially Continental isn't building the most robust pump out there. However BMW accepted this and can get away with this pump since most of the time you are past warranty when the failure happens. Pump from getbmwparts is around 411 bucks plus shipping and the thermostat is 91 bucks plus shipping. Also Continental has upgraded the pump for the 335 can't say if that is so for the 328.
I wish they would improve the life of this unit by potting the electronics and making the housing out of material that doesn't suffer thermal cycle failure. I would pay more for a pump that was basically going to last the life of the car. A Stewart electric equivalent.
I carry a new water pump in its box in the trunk of my E93 for this very special occasion. I am not aware of any remanufactured water pump suppliers out there but I can't see saving much money since the new pump seems much better.
One of our members lost his pump around 50K miles and the newer pump has taken him to well over 180K miles. He posted his repairs months ago and he drives a heavily modded car.
BMW does seem to have fallen down on the initial qualification of the HPFP, electric water pump, some fuel injectors. All have been improved but are still not at the reliability of your typical Asian auto manufacturers...
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