Ford Transit 52 reg TD280, over heating!?

hi, i was driving down the dual carriageway yesterday and out of nowhere my van slowed down and the temp gauge went to the hottest, as i slowed down the temp gauge went back down and now it just keeps on going up and down no matter what speed im going, the engine doesnt feel any hotter then normal or give of any burning smell, it makes a winding down noise when i switch of the egnition and i have to give it a few revs to start which it didnt need before this problem! any ideas anyone what this could be and the best way of fixing it? cheers for your time!