I had probs with mine too...only yours sounds alot worse. My car used to almost get to 3/4 on the guage in stop go traffic hot day. Thought this was problem. Started with thermostat, took it off checked it in near boiling water to check it opened fully (actually bought new one and took it back when comparedthe two in hot water and saw they both functioned the same). Then the radiator, thought maybe clogged. Took it out and got it flow checked at local radiator place (didn't even charge), found no probs (maybe able to do on car though but need to disconnect hoses). Found that cooling fan cuts in at just over half. Sensor plug located above gearbox on coolant hoses. If you pull that off the fan should activate due to the way the system is wired. After all that I didn't really find a problem. The car does get to about 2/3 on gauge intraffic, you can hear the fan kick in and the temp reduces back to about a 1/2. A guy I know had a problem with his head gasket that was causing his twin cam to overheat. Talking to other people the 4age does seem to run hottish to start with in the stock corolla application(correct me if wrong). Not as hot as yours is running though!! What I've said is all pretty basic but may give a few ideas. Good luck with it!