I own a 2018 Audi A5. Many critical cooling system parts - including the thermostat housing, water pump housing, radiator end tanks, breather tubes, and quick-connect hoses - are made of plastic and sit in constant exposure to coolant temperatures over 200°F. Over time, these components become brittle, crack, and fail prematurely. Recently, the plastic breather/return hose between the coolant reservoir and the radiator broke apart during routine service due to brittleness. When these parts fail, coolant leaks...
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quickly, which can cause sudden overheating, engine damage, and potential vehicle disablement while driving. Based on owner reports and my own experience, this appears to be a widespread issue across Audi/VW vehicles of this generation. I request that NHTSA investigate whether the use of plastic in these high-heat, high-pressure components represents a design defect that creates a safety hazard.