Your 1997 BMW e39 is overheating?

Answer 1

Check and replace the thermostat. Power flush the entire system from the coolent lines going into the firewall and also look into upgrading your water pump. Purchase the better thermostat, the one that stays open when it fails as to not overheat your engine and breech the head gasket. Also dril;l hte hole in the thermostat in the 12oClock position (research it).

Many helpful hints in the Bimmerboard: http://www.bimmerboard.com/forums/e39/

Also only get OEM or better parts, don't skimp on cheap parts that break, spend a little more now = less spent in the long haul.