If you want a temporary fix until you figure out the root cause, you can jump the two terminals for the aux fan at the temp sensor with a short piece of wire and it will keep the car cool, even if the radiator fan isn't working. That's assuming that your aux fan isn't shot. Also check the two fuses for the aux fan, they may be shot too.

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87 300D - Running on Veggie oil; 260,000 plus miles; Original #14 head