According to a mechanic, one of the two fans in front of the radiator (on the outer side of the radiator) died.

He said I could wait until the failure of the other, now operating, fan.

But I do not know how I can see whether one of the fans died or not.

I just opened the hood. Both fans were not rotating. Engine temperature gauge was at 87~90 degrees C.

How can I test these fans?

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1992 300D 2.5 turbo diesel. 319 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.