Don't bother to replace the radiator before you test it! Make sure it's bad first.

Do this simple test: take off the lower hose of the radiator. Block it with your hand, and fill the radiator with plain water. Take your hand off and the water should gush out in as big a stream as the lower opening. If it runs out in a smaller stream, the radiator has blockage inside and should be replaced or repaired.

Also, remember that a brand-new aluminum radiator is only $43 USD, but requires a bit of fitting.

wiki - Radiator

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A common cause of overheating is changing the coolant. With the A-series it is difficult to fill it fully. After a while of driving, when it reaches full temp the air will bleed off, so be sure to refill it after a full warm-up.