Check coolant temp -- should be 87 C or so. If not, bad thermostat. Easy to fix.
If the temp is OK, you have a bad temperature sensor -- this is why your aux fans won't run. Get it replaced, again easy. Could have a broken wire, too, althoug this is rare with a Mercedes (NOT with Volvo, though!).
You are running in open loop startup mode -- will kill your milage, your ox sensor, and your catalyst. Catalyst is expensive!
You may also have a bad fuel distributor if you have the older fuel injection system -- common problem. I don't know when MB changed to the LH type from the K-Jetronic. If the distrubutor is bad, it will be expensive to fix, and my mechanic has been having fits getting good replacements -- put three on a car before he got one that lasted more than 5000 miles! If it is bad, you will be trailing black smoke!
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!