rocitreal

strange. I also am having strange issues with mine. I love the car but its been in the shop for more time than I have had it over the 6 weeks of ownership. They are amazing but do not seem to be stress free...

E60I

I think the leak on the vent hose can only occur when the car is off and not circulating coolant through out the coolant system. Therefore, it might be difficult to detect while the engine is running because the coolant can flow to other hoses other than the "vent hose".

BimmerFan52

You are correct that the main function of the vent pipe is to provide relief for the closed coolant system pressure due to engine heat soak after shutdown, which drives coolant in the block to much higher temperatures than during operation.

Whether the pipe leaks during operation depends upon whether you have the coolant topped up all the way to the max line and what temperature the engine gets to during running.

I had read of the many failures of this part so before reinstalling the metal shield that covers the radiator, fan and vent pipe I started the engine and let it reach full operating temperature.

When at operating temperature the vent pipe started to drip slowly through a hairline crack. After I turned off the engine the drip accelerated, consistent with coolant overflowing the radiator and moving to the reservoir.