Diagnosing a Clogged Radiator
Internal restrictions in the cooling system are caused by coolant that has broken down and is no longer offering rust and corrosion protection. As seen in the illustration, rust can quickly clog the internal passages of the radiator. This alters the flow of coolant causing the engine to overheat. It is far more common with older cars, vehicles needing a coolant flush, and vehicles with used replacement engines. Inspect the radiator for external damage and use an infrared thermometer to find internal restrictions.
Infrared thermometers are helpful when diagnosing restrictions in the engine's cooling system. Coolant flows from the top of the radiator to the bottom. Move the thermometer across the radiator fins looking for changes in temperature. A restriction causes a drop in pressure resulting in a sudden change of temperature. The same is true for the air conditioning system. A kink or internal restriction in a condenser causes frost to form at the restriction. This is because the change in pressure has resulted in a change in temperature.