Coolant leak at the cylinder head flange — BMW 11 11 7 800 048

I noticed that my coolant was disappearing slowly but steadily. There was no obvious leak anywhere, and the repair shops couldn’t find one either. So I bought a pressure tester pump and pressurised the cooling system with the engine cold. It couldn’t hold even 0.5 bar.

I had replaced this pipe two years ago, together with the water pump. My mistake was saving about 30 euros by buying a Vaico replacement instead of the original part. Funnily enough, the original BMW pipe now costs 25 euros, while two years ago it cost 50.

The Vaico pipe probably started leaking almost right away, since I’d been noticing coolant loss for about a year. After two years it is slightly bent, which you can see in the photo below. I believe this is the main reason for the leak.

Its seal also has scratches.

I also tried bending it with my finger, and it does flex. Even the old BMW pipe doesn’t do that, so I think the plastic itself is different.

The new BMW pipe’s date stamp is not very neat, and there is moulding flash around the brass insert.

Here is a photo of all three:

Replacement

To replace it, you need to remove the fan and the alternator to get to the third bolt. The tightening torque for these bolts is 9 Nm.