Elec. fan runs when cold in A.M. 1990 300E??

[milhan]

Every morning, when I start my car to go to work, the electric fan turns on high. The outside temp in the a.m is usually between 60-70 degrees F. So its not exactly desert tempertures. After driving about a mile, the fan will turn off. After work when the temps increase to 85 degrees, the fan doesnt turn on upon start up. I dont have the A/C, or the ECON switch on. Any idea why this is happening? I worry when it gets below freezing this will happen, and my car will never warm up. Thanks 1990 300E. 3.0