I have BMW 323CI The Thermostat was replaced Upper and lower hose was replaced and now my antifreeze empties out and I have to keep filling it back up what could it be when anrifreeze empties out.
You may have a large air bubble in the system. Purchase an air bleed kit from your local auto store. If a shop did the work they should have done that. You may also have a bad cap on your radiator.
I vote bad cap or thermostat installed backward
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