Anyone had there Aux. Water Pump replace in 540i?

[Zowell]

Think my auxiliary water pump busted, and coolant is leaking from that section. Wanted to get an estimate on getting this replaced. If anyone has info, please help!!

[thejlevie]

The usual failure in the aux water pump is in the diaphram between the impeller and the motor, but there are quite a number of hose connections in the immediate vicinity of the aux pump & valve body. Any of those could be leaking, so check carefully before replacing the pump.

Replacement of the pump is not a difficult job and it is only about $110 for the pump. I clamp off the feed & delivery hoses and swap out the pump. It usually takes me longer to find and set two small needle-nose vice grips than it does to swap out the pump. Done that way a very small amount of air will get in the system, which will need to be bled out, but the coolant doesn't need to be drained.

As a workaround you can re-route the coolant feed directly to the valve body and bypass the aux pump. You can even leave it like that (disconnecting the power to the aux pump) at the expense of poor heat/defrost at idle.

[Zowell]

You can re-route to bypass the pump? Is that hard to do?

[thejlevie]

All that's required to bypass the pump is to remove the hose from the pump to the valve body and then move the input hose to the pump to that location on the valve body. If you do this do remember to pull the plug from the pump. I don't know if that would throw a CEL on an OBD2 car since the only ones I done that on were OBD1 cars.