A radiator can be tested to see that it will allow a sufficient amount of water to flow through it.
With the radiator full, watch the flow of coolant when the lower hose is removed from the radiator. If flow is sufficient, coolant should fill the entire radiator opening as it flows out.
Another test for radiator flow involves feeling the outside temperature of a radiator in various areas from top to bottom. If the radiator is allowing a sufficient volume of coolant to flow, the fins nearest the radiator inlet (the hose that goes to the thermostat) will feel hot to the touch. The areas near the radiator outlet will feel cooler. Cold spots indicate a restriction in the cold area of the radiator.
Cooling System Pressure Test
A pressure tester can be used to determine if leaks are coming from the radiator or radiator hoses.
When an internal or external leak is suspected, a pressure tester is helpful in locating it. Sometimes when trying to determine whether there is an internal leak or not, the engine must be tested at different temperatures. Cracks often leak when the engine is cold but not after it warms up. Also, although it is easier to pressure test a cold engine, leaks sometimes will not show up when the engine is cold. Test stubborn leaks with the engine hot and cold.
Pump the handle on the pressure tester to pressurize the cooling system to the pressure marked on cap. After five minutes, the pressure on the gauge should remain steady, which indicates no leakage. If the gauge pressure drops and an external leak is not apparent, an internal leak is indicated.
If the pressure reading drops during a pressure test, first look for signs of external leakage.
Check for external leaks at the heater core, heater hoses, radiator hoses, thermostat housing, core plugs, radiator, hole on the bottom of the water pump, and carburetor.
A pressure tester is used to test the pressure cap.