How can you test your radiator to tell if it needs to be replaced or not? What do you need to look for or can it be tested?
Assuming of course that it’s not leaking, warm the engine up to operating temperature. Then, without getting yourself caught in any moving machinery, feel all over the radiator. You’re feeling for spots that are hotter or cooler than others. If you find none and it’s still not leaking the radiator is fine.
Visually from the rear with the shroud removed or tilted away. White or green corrosion on the fins, tubes and tanks is a hint that it may not be in good shape. Missing fins between the tubes is bad. 5% missing and it is a definite change. 10% missing and the engine is running too hot. Pickup truck radiators which are usually bigger will last slightly longer than car radiators. I recommend looking at the radiator at about 100,000 miles and every year after that. When you notice that the temperature is higher than it used to be and there are no other problems with the way the car runs is another hint. You usually get hints.
If you take the radiator out, a radiator shop will flow test it for a reasonable price. For my case, it also included an ultrasonic bath and flow test for $40.00. (Black’s Radiator in MAryville, TN in 2002)