After car is warmed up and I driving down street I smell the coolant. My coolant level is little lower in tank but I cannot find the leak anywhere. No place on ground, nothing anywhere I can see. I smell it a little then it goes away. I can drive 50 miles, smell it a little bit for a few miles then it all goes away.
Help please

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2005 4.8is X5 Stock-be kind I am learning learning language