How to tell if a radiator is clogged

Written by jennifer patterson | 13/05/2017
How to tell if a radiator is clogged
By using a few techniques, you can tell if your radiator is clogged. (engine image by Tomasz Pawlowski from

A clogged radiator can lead to engine damage if it is not fixed promptly. Radiators keep the engine cool by transmitting the coolant through the engine block. The coolant is then heated, before being passed on through the radiator, where it is cooled by evaporation. When a radiator is clogged, there may be signs to indicate it. It is imperative that you repair your radiator as soon as possible to prevent extensive engine damage. You can tell if you radiator is clogged with some simple tips.

Park your car, and turn off the engine. Allow the engine to cool for 3 hours. Open the bonnet of the car, and remove the radiator cap from the radiator.

Start your car, and wait at least 2 minutes for the thermostat to open. The coolant will start to circulate.

Turn on your flashlight, and point it downwards into the radiator. Look for an uneven flow of coolant. If the radiator is blocked, the coolant will not flow evenly. Another quick way to check for a clogged radiator is to ask someone to rev the engine while you are squeezing the radiator hose. If the radiator hose stiffens and is difficult to squeeze as the speed of the engine increases, this means that the radiator is clogged.


Never open the radiator cap while the engine is hot to prevent serious burns.

Tips and warnings

  • Never open the radiator cap while the engine is hot to prevent serious burns.

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