Date registered: Jul 2004
Vehicle: 1991 500SEC 38,800 mi. 1987 560SEC Now 145K mi. (Spring 2017)
Location: Boston, MA area
Mentioned: 0 Post(s)
Quoted: 170 Post(s)
RE: 1986 190e 16v: overheating
At road speed, say 15 mph up, the fan doesn't really do much (if anything) for cooling. Just the movement of the car through the air creates the airflow across the radiator.
If the engine temp. is OK at low speeds, then rises to what you have described only at highway speed, I'd suspect perhaps the radiator itself (especially if original) is either partially clogged and cannot dissipate the heat into the atmosphere, or possibly the radiator fins are partially eroded away due to road salt/rain water.... same result.
Have you had the car tested for CO in the cooling system. Today a good shop can introduce a chemical into the coolant which will change color if combustion gasses are present. Head gasket, cracked head....
If your car was in stop and go traffic (I see the word 'freeway'.) when the car overheated, the fan operation would be the logical bet. I don't know what temp. it would activate on your car.
Now that the car has really overheated, were I in your shoes, I think I'd have the coolant tested for combustion gasses.
Good Luck, MBL