The later +8s did have a tendency to run hot and the fan seems to come on for long periods of time especially on the 4.6L. It maybe the sensor is too sensitive and cutting in early or perhaps there is a restriction in the water circulation. Radiators can become blocked if the incorrect ratio of anti freeze/inhibitor has not be maintained. I would be inclined to flush out the cooling system and add new inhibitor to see if that makes a difference.
Neil
