82 westie cooling system problems

[pipimilr]

Hi I am new to this site and I have looked over the past threads and haven't found what resembles my problem. I have an 82 1.6 turbo and she doesn't maintain engine temp. i installed a temp gauge and it reads 180 when it finally warms up, takes forever, but as soon as I head up an incline the temp goes up. my fan is operating. Then sometimes it drops temp down to 140. sometimes it goes up and down and does not stay at normal operating temp. I replaced termostat. I did put in some unmixed antifreeze when it overheated one time after it cooled down, could there be a pocket of antifreeze that doesn't get to temp, I just don't understand why it goes up and down. could I have a headgasket leak even though no oil in water or water in oil. I would like to drive this without having an adrenaline rush when I look at the temp gauge. Any ideas and help will be greatly appreciated. tell me what is the normal operating temp under all driving conditions. It seems to me that once it warms up that it should stay at that temp except for slight variations