My 82 300TD did this.
Check the radiator. If it is origanal it may be collapsing. If you have a thermometer, IR would be the best. Check the temp of the radiator at various places on it. Mine had the center section collapsing and you could "feel" a cooler spot in the center. If its this then its time for a new radiator. If its original then after 16 years this could be the problem.
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car