There are two types or compositions of radiators found in vehicles today: the all-metal radiator, found in vehicles since their conception, and the composite radiator, which has taken its place for the most part. It has plastic tanks on the sides and an aluminum core. The sides and core are held together with a crimping process. The biggest problem is that they crack easily. The cracks usually show up on the top plastic tank that spans the two side tanks. The cracks show up to one side or the other by the radiator cap, or by the crimping on the sides.
Lift the hood on the vehicle and make sure that the engine is cold. Remove the radiator cap. Fill the radiator with as much water as possible. This makes it easier to pump pressure into the radiator with the reduced free space.
Attach the coolant pressure tester on the radiator cap opening and turn the handle to tighten it down so it is leakproof. Pump the pressure tester and watch the pressure gauge on it. Pump it up to 15 pounds--no higher, since it could crack the radiator with more pressure.
Check the radiator on all sides and underneath for the leak. If no leak is detected, check the water pump, all hoses, the intake manifold, the heater core drain on the firewall and the freeze plugs. Check the throttle body if it is heated.
Check underneath the vehicle. If water is seen dropping from the front bottom of the transmission, the rear freeze plugs between the engine and transmission are leaking.
Repair as necessary. Pump the pressure tester up one more time after the repair to verify that it was a good fix. If no leaks are found, check the radiator cap for a bad rubber gasket and the spring for tension. Replace if damaged or defective.
