How to Troubleshoot a Noisy Radiator

Written by chris stevenson
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How to Troubleshoot a Noisy Radiator
Unique radiator noises will let the vehicle owner pinpoint the component failure. (Auto Engine image by Andrew Breeden from

A vehicle's radiator contains the engine coolant and dissipates excessive engine heat. It does this by circulating the water and antifreeze through a system of thin metal tubes constructed of aluminium or copper. Beside problems with leaking or overheating, a radiator and its components can produce some hard-to-interpret noises that can baffle the vehicle owner. Individual parts that have failed can reveal themselves with their own unique noise or sound, allowing the vehicle owner to pinpoint the source and repair the part.

Skill level:

Things you need

  • Radiator pressure tester
  • Gloves
  • Rags
  • Assistant

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  1. 1

    Fill the radiator or overflow reservoir to its limit. Drive the vehicle for an extended period of time, preferably on the highway for at least 30 minutes. Return home and park the vehicle. Place the shifter in neutral or park and the emergency brake set. Leave the engine running and raise the hood.

  2. 2

    Listen carefully to the radiator. Any thumping or knocking coming from the top of the radiator housing will point to a sticking or erratically functioning thermostat. This happens when the bimetal spring in the thermostat housing "shutters", periodically opening and slamming the vale shut.

  3. 3

    Listen carefully to the radiator for any hissing noises. Hissing denotes escaping radiator pressure, and can accompanied by a vapour or stream spray of coolant. Check the radiator cap for gasket integrity, the upper and lower radiator hoses for loose connections or splits in the hose, or any external crack or seam split in the radiator core or cooling fins.

  4. 4

    Listen carefully to the radiator for any clicking or rattling sounds. Examine the electric fan or fans inside their housing shroud. Fan shaft bearings that have worn out will allow the fan blades to hit the inside of the shroud housing. Check for any misalignment or wobbling of the fan blades. The electric fan motors must be replaced if such conditions exist.

  5. 5

    Listen carefully for a screeching or high-pitched hum coming from the top of the radiator. Examine the radiator cap. Look at the pressure release lever (valve) on top of the cap. It should be in the "down" position flat against the cap. Push it down. If it refuses to seat and pops back up again it means the hold-down spring inside has weakened. Replace the radiator cap.

  6. 6

    Let the engine cool and remove the radiator cap. Start the engine. Listen carefully to the radiator cap inlet for any churning or bubbling sounds. Let the engine idle while doing this or have an assistant "rev" the engine several times. Look at the overflow reservoir and listen for any bubbling sounds by removing the cap and inspecting the inside. Any bubbles that come from inside the radiator or overflow reservoir indicates exhaust gases have entered the water passages in the head. This symptom will point to a blown head gasket or a warped or cracked head. Repair as necessary.

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