What this usually means
On BMW G30 520i/530i, coolant loss is commonly expansion tank, hose, water pump, or thermostat housing before it is a head-gasket issue. Pressure-test the cooling system and inspect plastic fittings before approving major engine work.
What to ask the workshop before approving repair
- • Show the diagnostic fault codes.
- • Show photo/video proof of the failed part.
- • Give an itemised quote for parts and labour.
- • Explain why cheaper common fixes were ruled out.
- • Use/confirm: ISTA
- • Use/confirm: Cooling system pressure tester
This is not a final diagnosis. It is a money-saving checklist before you go workshop.