scottalexander

Good work finding the power drain.

You mentioned you could hear the water pump when the engine is turned off. In the summer that is more natural for the pump to operate for a short while when the car is turned off. I have not heard of a water pump being the parasitic drain on a battery.

I wonder if the real drain problem is something up stream because the water pump is not that old (e.g. relay, thermostat, coolant sensor, etc).

I recently replaced my water pump, thermostat, U hose and the mickey mouse hose on the front of the block that terminates on the thermostat.

You can do this entire job for $300.

neilv

It it is winter and below freezing here so I wouldn't expect to hear it when the car is off. Especially after an hour and when the car should be asleep.

I will be checking the sensors today/tonight (plug in water pump and unplug sensors). Do you happen to know the location of the water pump relay? not much info in it online.

Because the car as 190k km on it I'm going to just do all the coolant hoses as well as the WP/Thermostat and get that out of the way; cooling systems are BMW weak points. For me being Canadian all that will be about 1000 (shop cost). I wonder If they cheaped out and got a off brand WP or something(I'll get under the car to find out) and I'm sure this is why they sold the car cheap.

I also did this whole job on my N54 335 plus the turbos and other stuff, so unless x-drive makes my life a pain; should be easier.

scottalexander

Let's do some research on the water pump upstream operations.

The electric coolant pump is controlled by the engine control module (ECM).

Engine load, temperature, operating range are used by the engine management system (DME) to determine coolant pump operation and speed.

Is it possible your coolant sensor or something else is throwing bad data to the ECM?

If your pump was really faulty. We could see fault codes stored in the ECM.

neilv

Btw thanks for working with me on this. I can rebuild motors and everything else mechanical all day long but electrical non sense is my nemesis. Funny I've had my N54 car for years without any real issues but this I've had for a month and all the extra electronics are whats causing me grief.

I figured the ECU controls all of that but that's a hard diagnosis and probably the most expensive. There's a WP fuse in the ecu box; that was good (the WP operates just as it should so I figured). I haven't been able to find a specific water pump relay either.

When I'm home, I'm going to plug in the water pump connector(which was zip tied on btw) and disconnect the 2 coolant sensors, wait an hour: if the humming stops its the sensors/ if its still there then its the WP.

Only code I'm getting is AWD/DSC related so nothing engine related; Wondering if just bad/cheap electronics in the replacement WP that just sucks power

scottalexander

We knew the water pump fuse was good because the pump ran continuously to drain the battery.

The eBox under the hood is notorious for electrical problems due to water entering that box. When you were in the box did you see rusted wires, corrosion or anything odd?

Next:

In a perfect world, the water pump only does what its told to do. If its getting power and instructions from another source (and running while the car is off for long periods) I'm inclined to look at those other sources.

You said the water pump plug was zip tied. Does that mean the connector harness is faulty? Is it possible the fault is at the harness male connector pins?

neilv

So just got to the car. Its been asleep for a few hours now.

Plugged in the water pump and 3 seconds later it starts right up. Unplugged the 2 temp sensors and it stays on.

The connector looks to be broken on the locking tab part; explains the zip tie

scottalexander

If the car has been asleep, the engine is not hot.

You did the sensor test and the pump still runs.

Next idea:

Forgetting to reconnect the electric fan or it disconnected somehow can be causing the pump to operate. Why?

Let's say the fan connector or wiring is faulty, this could trigger the coolant pump to run to prevent overheating.

Check the fan ecosystem elements ( fan fuse, fan relay, wiring, connectors, etc).

Can you get the fan to turn on?

neilv

The fan was plugged in. Unplugging and plugging back in made no change in either state; Wiring/connectors show no sign of damage or tampering.

Also unplugged the fan fuse(big 60A in the glove box) and no change.

Still trying to source the fan relay location in the wagon

But I did just double check and the fan works

scottalexander

New ideas:

Don't run the vehicle for a while so the engine is cold. Now go to the trunk fuse box above the right rear tire. Put your finger on the outside of terminal 30g relay. Is it cold? Is it warm? Is it hot?

If the water pump connector was unplugged, reconnect it now. Presumably the water pump will start and continue to run as it did before. Let it run for a while. Now go to the trunk fuse box above the right rear tire. Put your finger on the outside of terminal 30g relay. Is it warm? Is it hot?

Next:

If the thermostat electronics were malfunctioning could that be the culprit? Disconnect thermostat connector and run that experiment.

Next:

Does the pump stay running when the car is locked? What if the car was unlocked?

Next:

Inexpensive fall back plan worst case scenario:

When you unplug the water pump connector you can see the thick, red wire on the harness. Wire in a switch and run it back to the dash board (allowing you to turn off the water pump from the cabin) up until you crack the code on the culprit.

neilv

It was the water pump. Ordered one on the hunch (cant get parts on weekends from my source); Just plugged it in and didn't start running. Have been able to start the car in the morning without jumping it for the first time.

Thanks for your help running through this