In addition to the excellent information from Chris above:
Any temp between 80C and 100C is perfectly normal. The newer cars (and even some of the older ones) DO NOT necessarily park at 85C all the time like your dad's 1980 300D may have done. Also, the temp sender tends to read low with age, so those of you who think your old car runs at 85C all the time might be in for a shock if you bought a new $10 sending unit.
More typical is 85-95C under most conditions. Up to 100-105C is fine if the engine is under heavy load, and/or ambient temps are high. However if it's going past 100C on a regular basis, that's not good, and if you see 110C+, that's definitely not good... time to figure out what's wrong (dirty radiator fins? bad fan clutch? coolant flush needed? bad t-stat? etc, etc...)
