This question is on my 1992 300D 2.5 turbo.

I suspect the viscous fan clutch is bad or going bad. WHen at idle, the temperature would rise, when the car is in motion or when i rev it, the temperature falls. Is there any way to test it without removing it?

When i turn on the heat, the temperature falls, when i turn on the A/C the temperature rises.

thermostat replaced, coolant flushed, nothing changed....