New expanssion tank craked and leaking coolant. Overpressure?

[juribe2]

Hi,

I need you advice again. About 6 months ago I installed a new expansion tank, new pressure cap, new hoses and new thermostat on my M104 engine. I also installed a new radiator about 1 month ago.

Now, the new expansion tank is cracked and leaking coolant thru those cracks. There is a long longitudinal crack and 4 spot cracks.

Do you think I got a defective tank or do I have some overpressure in the system (pressure cap is also new and identical to the old one). I also notice that the upper radiator hose increases diameter when the engine is hot (a little inflated).

Do I need to get a new tank and cap or is is something different?

BTW, parts for this car are getting hard to get. This tank is not available online and the intake air temprature sensor is also out of stock in every online store.

Thanks !