This may not be at all related to your problem but it would help you to try:

The twin electric fans at the front would come on (with or WITHOUT the A/C) to keep the engine temperature at check.

Those fans have a five stage (if I remember correctly) speed setting that will eventually come on as the engine temperature rises (for any given reason).

When you check the OBDII codes (on my car, I think your 1995 has an OBD-I) with the computer, there is a procedure to test the five settings (or speeds) of the electric fans.

If any of the speeds is not working properly, it will pop a failure code. If you have a failure on the lower speeds of the fans, they will not come on to lower your engine speed unless it is really hot (+110°C).

Here it tends to be hot and humid in certain places and the twin electric fans work at their lowest speed setting (very silent, you have to check them from outside the car to hear them) most of the time.

Now, what puzzles me is that at highway speed your temperature will not lower ??? If you find out your problem, please don't forget to post your solution.

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]