The light you are seeing it NOT an overheating light, it is a low coolant light. Check coolant reservoir if it is at least half full, the coolant level sensor, a float, might be bad. I would recommend using either the MB coolant or Xerex G-05 coolant available at autozone, available, advance, O'Reily's, etc. Both are very pale yellow in color. Xerex is cheaper than the MB antifreeze and is accepted as MB compatible.
80 is completely acceptable for a driving temp, even 90 to 100 is fairly normal.

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Christopher Henkel
1990 190E 2.6 - Arctic white SOLD
1986 190E-16v - Blauswartze
1993 300CE - SOLD
2003 W208 CLK 320 Cabriolet - Magma Red