BMW E46 Expansion Tank Cracking and Cap
E46 expansion tank cracks, is it a common fault?
Yes. The plastic expansion tank often cracks and is considered a weak point of the E46. The leak usually starts at the seam or at the joints at the ends. A damaged tank is replaced with a new one, and a repair does not last long.
What is the correct expansion tank cap pressure?
According to BMW, the cap pressure is 2.0 bar. The cap does not determine the system pressure but only releases overpressure. With a cap of too low a pressure the car may boil over. An old cap that does not release pressure can crack the tank, so a new cap is cheap prevention.
What should be replaced together with the expansion tank?
Replace the cap at the same time. The plastic connector of the upper radiator hose on the end of the tank can break, so check it. Because of ageing, the upper and lower radiator hoses, the water pump and the thermostat housing are worth replacing at the same time. After the replacement the system is bled.