How to Test the Pressure of an Auto Radiator

Written by chris stevenson
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How to Test the Pressure of an Auto Radiator
Use a radiator pressure tester to check the radiator and cooling system on your vehicle. (Auto Engine image by Andrew Breeden from

A vehicle radiator consists of core tubes, radiator cap, fitting necks, cooling fins and bottom and side tanks. Radiators come equipped with aluminium or copper construction or a combination of plastic and metal. Plastic bottom and side tanks are found on some of the newer domestic or foreign-make automobiles because they resists rust and weighs less than the metal varieties. Radiators work under a slight pressure measured in pounds. Heat and boiling cause the pressure. The higher the temperature, the higher the pressure rises. Excessive pressure can cause seam cracks and pinhole leaks. Checking the radiator pressure also runs leak tests on all the other cooling system passages and components.

Skill level:
Moderately Easy

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Things you need

  • Floor jack
  • Jack stands
  • Plastic
  • Duct tape
  • Owner's repair manual
  • Old blankets
  • Rags
  • Lithium grease
  • Pressure tester
  • Shop light

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  1. 1

    Take your vehicle to a car wash, and open the bonnet. Use plastic to cover crucial electronic components such as the alternator, distributor, cold-air intake and any exposed electrical sensor. Pressure wash (with soap setting) the engine and radiator on the top sides and bottom, removing dirt and oil from the radiator fins and engine block. Rinse with clean water. Remove the plastic and tape. Drive the vehicle home.

  2. 2

    Place the shifter in park, for an automatic. Place the shifter in neutral for a manual transmission. Apply the emergency brake. Remove the radiator cap. Fill the radiator to the top limit mark, which will be just under the bottom of the filler neck. Fill the plastic overflow tank reservoir to the prescribed limit.

  3. 3

    Use a floor jack to lift the vehicle, and place four jack stands under each corner of the frame. Place some old blankets under the vehicle to catch any leaking water. Open a radiator pressure tester kit, and read the directions. Make sure the engine has cooled. Pick the appropriate adaptor that fits over the inlet neck of your radiator. Screw the adaptor to the radiator neck.

  4. 4

    Use the pump handle on the pressure-testing tool to bring the pressure to 4.54 Kilogram, or look at the pound pressure rating on your radiator cap; if it reads 5.44 Kilogram on your radiator cap, pump the tool until the gauge reads 5.44 Kilogram. Refer to your owner's manual for the cap pressure if the number can not be read on your cap face.

  5. 5

    Use a shop light to examine the upper and lower radiator hoses, the radiator drain plug, radiator tank seams, underside of the water pump and heater hoses. Refer to your owner's manual for the cooling system components and routes. Look for coolant leaks at those points.

  6. 6

    Let the pumped pressure remain in the radiator for at least 20 minutes. If the pressure drops and you can not find any external leaks, you might have a defective intake manifold or head gasket. Check the heater core under the dashboard to make sure it has no leak and has not wet the carpet.

  7. 7

    Remove the pressure tester adaptor, slowly releasing the pressure. Insert the adaptor extension in the kit into the radiator fill neck by twisting it in. Wipe the inside of the radiator cap clean with a rag, and smear a small amount of grease on the copper cap gasket.

  8. 8

    Screw the radiator cap onto the top adaptor extension. Pump up the pressure tester to the correct poundage, per your owner's manual. Listen for air escaping from your radiator cap, or look for any signs of leaking water from the radiator cap gasket or pressure relief valve. Allow the pressure to hold for 20 minutes. Look for any drop in pressure, which will indicate a leak.

  9. 9

    Raise the vehicle with the floor jack, and remove the jack stands. Replace the radiator cap.

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