If you discover a loud rattling noise or a tappety sound coming from under your bonnet on the driver’s side; your supercharger could be the culprit. The M45 Eaton supercharger found on the MINI Cooper S is different because it has two separate oil filled chambers. The front noise cone has 145ml of supercharger oil capacity while the rear has 40ml of supercharger oil capacity. What is often the route cause of these supercharger failures are the bearing seals letting go. Once this happens oil goes through past the bearing and then into the inlet track.
The back of the M45 supercharger drivers the water pump through a fork gear known as a Power Take Off (PTO). Once the cavity holding the 40ml of supercharger oil runs dry the gears start to eat themselves. If this is not remedied quickly the problem accelerates very quickly, until the water pump does not turn and your car overheats leading to more headaches.
In this picture you will see one of water pump gears still installed and the location of the seal behind it that regularly fails! The gear doesn't look that bad however notice the huge amount of iron filings left; it almost looks like sand or soil. This chamber should be clean and the colour of the aluminium housing visible! Instead everything is caked in rusty iron filings produced form the gear grinding!