How do I locate leak in cooling system?

[Benny318i]

I have an '04 318i which has been bleeding coolant slowly for the past 3 months. My mechanic could not locate the source. I've already replaced the radiator and the two parts pictured below. I still have to top up about a liter of water every few days.

How do I locate the sourcr of the leak?



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[dchitiyo69]

Is the low water level indicator comes on before topping up? YOU need to run your engine till temperature is high to normal running temperature. Park it on a clean pavement or surface to see if there are any drop from the engine compartment. Switch off the Engine and quickly listen to an hissing from the engine compartment. Things to check. 1. Expansion Bottle condition ( Might have a hair line crack) 2. All connections to the bottle. (Might need to change O-Rings) 3. At the back of the Engine there is a cover which has two O-Rings these might leak at high pressures. (Change O-Rings)

[damo318]

+1 on the expansion tank it's a common problem