White smoke from tailpipe when driven fast, why

So white smoke means steam i.e. water, Black smoke is gas, blue smoke is oil. Are you sure the smoke isn't blue? Valve stem seals would be blue smoke. I would check the intake manifold for signs of oil residue by removing the throttle body first. If there's some oil reside I would check the oil separator/crankcase breather system on the back of the manifold. If the valve stem seals are leaking you can either live with the smoke or get rid of the car as the repair would cost more than the value of the car. I hope this helps, Kind regards, Stephane Grabina BMW Excluservice Rockville, MD 20852 www.bmwexcluservice.com