According to Mike Miller preventive replacement of waterpump every 60k and radiator every 90k, though the V8's have/had less cooling failure issues than I-6's.
BKing has it right! Also keep an eye on the plastic along the top where the hoses enter and exit... it tends to be a weak area and will be the first place you will see trouble. Otherwise, enjoy that beautiful car! Ours has 166K and we will gladdly put a third radiator in it when the time comes
As we know, Mike M. suggestions are really spot-on. The steps I follow for my 540i and e34 525i are: use only BMW antifreeze, replace the radiator at about 75,000 miles and the water pump at about 50,000. Thermostats should be replaced whenever one or the other items above are done. I've gone through plastic thermostat housings at regular (mine) maintenance levels and never had a problem, but the upgraded aluminum ones seem logical. Good luck.
