hiya, my 1995 volvo 960 estate drives fine and all, but recently I noticed that she overheats, she is fine if driven "normaly", even for 2 hours on the motorway, but as soon it gets up a wee hill, she overheats very quickly right to the red area. she cools down as soon as the road is streight with heating on full blast for a moment, than she is fine again. does not loose water, van runs, what could it be? thanks for any suggestions in advance