Question: how do you know when your radiator is clogged?
Answer: Leaking coolant. When coolant is not able to circulate in the radiator, it can leak out onto other areas of the vehicle. ... 
Discolored and thicker coolant. You know your coolant's original color, don't you? ... 
Damaged water pump. ... 
Excessively high gauge temperature readings. ... 
Blocked, bent, or damaged radiator fins.