I drove my car for about a year with no fan (P/O removed it for unknown reasons) and I only ever had problems when sat in traffic for more than 5 minutes. The temperature would slowly creep up, and I would have to turn the heater on and rev the engine (no aux water pump either) to bring it down. I've since fitted an electric fan which I can turn on with a switch from the drivers seat.

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1991 W124 250D - 130k Miles