What this usually means
On G20 318i/320i/330i, coolant loss is commonly expansion tank, hose, thermostat or water pump before head-gasket failure. Ask for a pressure test and visible leak trace 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.