escort mk2 temp gauge shows overheating

[gnilrac]

Hi,there!Thanks for viewing my problem.I have a 1980 escort mk2,automatic transmission.My problem is the engine overheats fairly quickly,and not even strenuous driving.The waterpump appears to be moving the coolant as I can see it moving when the radiator cap is off.There is a small hole in top of radiator,about,1mm ontop.Can that little hole cause it to overheat so quickly?Any advice would be appreciated.