Why Pressure Test an Engine Cooling System?

Any time you open up and reassemble the cooling system, you should pressure test the cooling system to check for leaks. This is usually the next step after a cooling system flush. The pressure test can also be carried out if a leak is suspected.

Why pressure test an engine cooling system?

Pressure testing is used to check the cooling system for leaks and to test the radiator cap. The most common pressure tester is the hand pump with adapters to fit different size caps and the radiator filler neck.

Another type of pressure tester uses shop air connected to the coolant overflow hose. A third type has an adapter that replaces the radiator cap and allows the insertion of a pressure or temperature probe. Workshop air or simply the pressure generated by the coolant system can be used to measure the pressure and check for leaks.

Pressure Test An Engine Cooling System

How to Pressure Test the Cooling System?

You use a pressure tester for the cooling system. If you don’t have one, rent one from your local auto parts store. It will come with instructions.

Generally, it attaches to the radiator where the radiator cap goes and you pump it by hand until the pressure on the gauge matches the pressure that is written on top of the radiator cap. Typically, on a modern vehicle, this pressure is between 13 and 16 psi.

Leave the vehicle at this pressure for 20-30 minutes. Then inspect the entire cooling system for leaks and check the pressure gauge on the pressure tester for a change in pressure. If the pressure is lower than before, there is likely a leak.

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To test the system using a hand pump tester, make sure the radiator is full. Use the correct adaptor and connect it to the filler neck. Attach the pressure tester to the adaptor. Slowly apply pressure to the system up to the range of the system or the range shown on the radiator cap. The system should hold pressure for at least two minutes. If not, check for leaks in the system.

To test the radiator cap with the hand pump, attach the cap to the pump using the proper adaptor and operate the pump until the cap starts to release pressure. Note the reading on the cap to see if it is releasing at the proper pressure. Stop increasing the pressure. The cap should be able to hold this pressure for approximately one minute. If the cap releases early or late or does not hold pressure, replace the cap.

To test the system using shop air, install the adapter with the pressure probe. Connect the shop air and increase the regulator setting to the pressure rating for that system. After the pressure is reached, shut off the shop air. The system should hold pressure for two minutes. If the pressure drops, then check the system for leaks.

If no external leaks are found, always consider the possibility of a failed head gasket allowing coolant leakage into either the cylinders or the oil passages.

Other items to remember regarding the cooling system:

  • Never open the cooling system when the engine is hot. The coolant will burn you.
  • A cooling system flush can be performed about every 100,000 miles on modern vehicles or sooner if the coolant is dirty upon inspection.
  • A cooling system flush and/or repair of a leak in the cooling system may not correct an overheating issue with the engine. This should be checked by a professional.
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How much does it cost to pressure test heads?

It will cost approximately $1000 for a reputable compression test done by the technician. The reason is, that each injector must be removed and replaced with a new gasket. At this time, you must also put the brake on. 5-6 hundred dollars is all that is needed for that.

Will a coolant pressure test show a blown head gasket?

If you suspect a head gasket failure, the scientific test is to check for combustion gases in the cooling system. This test will show if the compression has leaked into the cooling system, and therefore if the head gasket has blown.

What is normal cooling system pressure?

Depending on the model, this pressure can range from 4 to 30psi (30 to 200 kPa). The pressure relief valve allows excess pressure to escape when the system pressure increases with the temperature.

What causes no pressure in the cooling system?

The most common cause of radiator leaks is leaky hoses, but you can have leaks in the radiator itself, too, which can be a bigger problem. The coolant continually running from your radiator to your hot, running engine and back again creates a lot of pressure.