Losing Coolant E53 3.0D

[Bargain Bucket]

I have to add 1/2 a litre of coolant every couple of hundred miles now. It's slowly getting worse. No signs of a leak (no white stains on any visible pipework, no puddles, nothing) so I'm going to have to replace parts until the problem goes away. I hate doing that - it's so amateurish. Expansion tank cap and vent screw have already been replaced so onto the expansion tank itself next. Is there a recognised decent aftermarket unit available (Behr, Hella etc) or is it best to stick to BMW? I'd have thought a decent brand aftermarket should be fine.

If that doesn't fix it then onto the waterpump and thermostat.

Thanks.

[shadrack]

just get someone good to look at it, why people just replace everything is beyond me, a leak can be found

[Nat]

+1 on the test.

Do a pressure test...........You'll get your answer.

[ayat]

please update how you get on, ive had a coolant leak for as long as i have owned the car, ive given it to one of the best bmw specialists and my own mechanic to no avail. no visible signs, pressure tested hot and cold, but im having another look at it now with the winter months coming it seems to lose more than when its warm, so something to do with expanding in the heat and helping the leak.