Mondeo V6 tensioner.
A V6 Mondeo came in for a routine service and it was noticed that the water pump belt had been getting very hot. On closer inspection we found the tensioner pulley for the water pump belt wasn’t actually turning, but the belt was being dragged across it. Once it was removed the problem was obvious, the bearing for the tensioner wheel had collapsed, so the wheel no longer turned. If left any longer, the belt would have snapped, which wouldn’t have been obvious to the driver, but would have meant the water pump would have stopped turning, and subsequently the engine would have very quickly overheated.