It seems pretty basic to me here. Monitor the water temp going into the radiator. Then monitor the water temp coming out of the radiator returnimg to the block. Is there the proper temperature drop? Not ok means an air flow problem (should hear the fan roaring on high speed)? If this all ok then engine is retaining too much heat inside the block.
Next I would pull the water pump, maybe vanes set for one operating the wrong direction? Dumber things have happened. Thats where I would go.
Would be interesting to know the previus owners histories.
