Loosing coolant and heater playing up

[bendy]

2009 320i E90 LCi N46B

First of all I noticed that the driver side was not getting any heat through the air con. Passenger side is working fine. I get occasional fogging on drivers window. But.. occasionally heat will come through in the drivers side.

A few weeks later I started getting low coolant level warning.

Ive has no obvious water leak. Ground is dry underneath. Interior is dry.

On a low fan speed, I guess because it is quieter, I can hear gurgling and a hooping noise every now and then through the vents.

I can drive for hours without ever overheating or loosing water. But once the car has been left to cool and restarted that’s when the coolant level is low.

If I drive for a little bit with the low level alarm then stop and start the car then the level has come back to normal.

Usually I always refill the overflow tank when it alarms low and it would usually take about 500ml.

6 months ago I replaced the radiator. I have a few times bleed the system just by run the engine with bleed screws open.

Mechanic has has done a pressure test which holds strong. He has done a TK test and there is not evidence of exhaust gasses in the water.
No error codes.

This is a really frustrating and confusing problem. Does anyone have any ideas?

[White94RX]

Does the N46 have an electric water pump, same as the N52? If so, it has to be bled properly. It's not as simple as opening the bleed screw with the engine running. You have to turn the pump on, and it runs the pump for about 12 minutes at varying speeds. So fill it properly, perform the bleed routine, then see what happens. Heater cores are known for clogging on E90 vehicles.

[bendy]

Does the N46 have an electric water pump, same as the N52? If so, it has to be bled properly. It's not as simple as opening the bleed screw with the engine running. You have to turn the pump on, and it runs the pump for about 12 minutes at varying speeds. So fill it properly, perform the bleed routine, then see what happens. Heater cores are known for clogging on E90 vehicles.

I spent days trying to get my aux water pump running to be told I don't have one, apparently..
With a blocked heater core I would think I wouldn't be getting any heat at all coming through..?

[White94RX]

I'm not talking about the auxiliary water pump. I'm talking about the main water pump. The N52, 54, and 55 have electric water pumps, and not a belt driven water pump. We didn't get your engine here in the states, so I don't know if it has an electric pump or belt driven pump.

And the heater core can be partially clogged or blocked, giving different temps left to right.

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