97 Achieva overheating issue.

Last week the upper radiator hose ruptured, so I replaced it and the lower one. Now after driving it all week, randomly the temperature gauge likes to move up and down for no reason. Sometimes it'll heat up while I'm idling, other times when I'm just driving. The low coolant light is on but it's not because of low coolant, the mech I took it to didn't burp it properly. But anyways last night I took a friend home, on the return trip back I looked down at the temp gauge and it was in the red. (in between the thinner red line and the thick red line) I was just wondering if anyone had some insight on this problem, and if that happening messed up my car for good, thanks.