The coolant expansion tank is a very common failure. The engine coolant system is under pressure during operation. Pay close attention to leaks around the coolant reservoir, item number 17 13 7 529 273. If there are any defects in the coolant reservoir it is recommended to replace the tank before a catastrophic failure occurs, which may lead to coolant loss and costly engine damage. A visual inspection to the engines cooling system is easy to do, If you know what to look for! (follow the steps below)
4. The coolant leak is mostly visible from the bottom side and may go unnoticed in the driveway. This is often due to the fact that the system is under operating pressure while driving. Once the vehicle is turned off or left sitting overnight the vehicle is slowly bleeding pressure off and may not present with a leak until there is a catastrophic leak. This is why a visual inspection is critical. Watching for a "low coolant" warning light or finding that you have to add coolant from time to time is an indicator that something is definitely wrong.