I have a bmw x3 2004 i have problem why every 2 days i have to put coolant???

I,ve put new coolant tank and mine still does it

The expansion tank is a common problem that is caused by the thermostat getting stuck, then releasing high pressure water into the expansion tank. This causes the tank to eventually crack. Make sure to change the thermostat along with the tank. If this isn't your problem check the top and bottom hoses... if this isn't the issue the next is this to check is the water pump.