Tech Tip – Inside The BMW Electric Water Pump
Just replaced an electric water pump on a newer Maine BMW 535 wagon this morning, quite a interesting work of technology! Most cars, including older BMWs, use a water pump which is driven by a belt on the front of the engine, a tried and proven design, but not one which allows dynamic control. As it has transitioned from the older “M” engine to the new “N” designs, BMW has come up with an interesting twist, an electric engine coolant/water pump.
An electric water pump is really a brilliant idea, it offers a higher level of control of the engine operating parameters. The electric pump can be turned on and off as needed to speed up engine warm up time and precisely control engine temperature. As an additional benefit the parasitic drag of a belt driven water pump is eliminated, in theory improving engine performance and fuel economy. Anything mechanical can fail, and the electric pump on this vehicle experienced just that, a failure of the electric motor to rotate the pump impeller and circulate the engine coolant.
Since this is a very new design, and few have seen the internal construction of the pump, we thought a photo documentary might be in order here. You’ll note the pump impeller is labeled “VDO”, a long time supplier to most of the German manufacturers. You may also note what appears to be a NiCad battery, could also be a large capacitor, inside the pump electronics. This really caught our eyes here, and we’re in the processing of determining exactly what the purpose is. The capacity would seem to be too low to run the pump, but we’re sure the engineers at BMW have a reason.