E46 318i - Broken Coolant Hose! [11537572158]

 After about 650 miles in the E46 Touring the radiator light came on. Just the amber warning, to let me know it was getting low, not the red warning when it is running out and I refilled about 1.25 litres of water / coolant to the engine. This seemed about right to me, as I feared it may be using a bit of water and there was plenty in when I bought the car so 1.25L in 650 miles isn't catastrophic and can be lived with.
About two weeks later the radiator light came on again and I dutifully refilled 1.25 litres, but the car had only covered 120 miles so I knew something was now amiss, only for the light to come on yet again after just five miles of my six mile round trip to work. Under the hood with the engine running I could see a huge pool of water in the under-tray and a drip, which after much tracing turned out to be coming from a slim rubber hose that connects to the left side of the cylinder-head [N42 engine]. It was a constant drip, but when I wiggled the hose-end the coolant began to spray round the engine-bay, so here was the culprit. Turns out the hose-connector into the head was completely sheared off, as you can see in the pic, and should extend about half an inch into the housing. The only thing holding any water into the upper engine at all was a single M6 thread screw.

The hose in question was BMW Part No. 11537572158, shown in the diagram connecting the thermostat to the cylinder-head. This is a common fault I am told on N42 and N43 engines, along with several other coolant hoses that have plastic end connectors, particularly in the US where kits can be purchased to convert the brittle plastic ends to aluminium ones. This seemed unnecessary for me, given the cost of a replacement part and the age of the car.

As there are so many coolant hose variants, finding the right used OEM one on eBay and the like can be difficult, but they do pop up. I was able to get a new spurious part through work for just £18, but I'm sure commercial motor factors will not be much more expensive as long as they have stock. Spurious hoses tend to come with a new rubber O-ring fitted. BMW dealerships will charge a premium, but at least fitment is guaranteed and they are revised parts, though these may not come with the rubber O-ring which will also need to be ordered.