There is another current post entitled "radiator". I copied some appropriate text for you.....
The mix of water to antifreeze IS important! The antifreeze extends the operating temperature range of the water but it does NOT remove heat, the water does that part. Make sure that you have a 50-50 mix.
You could very well have some clogged passages in that radiator. Have you tried flushing your system yet? Buy some radiator flush and follow the directions on the bottle. For the effort to do this though, I'd just as soon perform a back-flush which will require cutting one of your heater hoses and installing a T-fitting to accept a garden hose. Everything that you need to do this comes in a kit. It's easy to do and the results are much better than just running flush through the system alone. Check it out at an auto parts store.
If at anytime in the past a previous owner used that radiator stop-leak stuff, it may have stopped more than just a leak, it may have stopped water flow though passages in the radiator. If that's the case, even back-flushing won't solve what only a new radiator can. Be ready for that possibility.
Check this out too; When you're tooling along and the temp gauge is up there, turn your heater on. This should lower the temperature since the heater core is nothing more than another little radiator. Try that and see what happens.
On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"
'68 Sprite 1275
'76 Midget 1500