I'm losing coolant but i'm just wondering if there are any usual suspects that might fail on an '05 Cooper.
I'm still getting hot air through the heating system, which I guess is a good sign, and the exhaust doesn't appear to be blowing out water so I don't think its a head gasket fail.
radiator get damp around edges.
water pumps can leak only when car at running temp under load pink traces under it is a sign,
most common is header tank spit,
also most common the thermostat filler neck and the screw top can leak,
they are a total pain to bleed, have found front pointing down hill on the gen 1 helps with passengers side slightly higher than driver side, and keep it idling and drip water in to the filler neck but dont totally fill as such this allows air to escape with out water escaping as such,
below is link for head gasket test kit if in doubt, its common around 100k for head gaskets on gen 1 tritec engines https://www.ebay.co.uk/itm/BT-3-BLOC...UAAOSwLEtYi8Gi
if you can afford it might think about using water less coolant its so much better at control temp and pressure as no water in it so dont expand like water coolants do,with car at running temp can remove radiator top and no explosion of water and steam its really that good, below link https://www.evanscoolant.com/