Your aux fan should run in high speed and blow like crazy -- if not, may be time for a new (or "recovered") one.
Test the fan clutch by listening at startup -- should make a roar that goes away in a couple seconds. It should also begin to roar when the clutch engages at about 100C, and move lots of air. If you shut the engine off when it's plenty hot, the fan should stop in less than a single rotation. If it spins much, the clutch is shot.
How old is your water pump?
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!