How To Pressure Test Your Car's Cooling System

How To Pressure Test Your Car's Cooling System

12th Feb 2019

The pressurized cooling system in your vehicle won’t work well if it has a leak. You can find any leaks by doing a cooling system pressure test.

Most cars, trucks, and SUVs made within the past 20 years have a pressurized cooling system. This consists of a radiator, radiator cap, hoses, fans, and a water pump. The system transfers heat from the engine and out through the front of the radiator via the fans. Modern automotive cooling systems contain coolant. This becomes pressurized as the engine warms up. Without pressurization, the system won't work as intended.

Cooling System PSI

Automotive cooling systems support a specific amount of pressure. A typical vehicle's cooling system can support 10 to 15 pounds per square inch (PSI) of pressure. Once the pressure exceeds this limit, added pressure is released to the coolant reservoir.

How Pressure Is created in a Cooling System

This happens when the engine warms up and, subsequently, heats up the coolant. Coolant, like most liquids, expands when it’s hot. Because automotive cooling systems are closed – they don't allow air to escape – the coolant can't expand. Instead, it becomes pressurized.

The coolant continues to expand and pressurize as it heats up. It will eventually reach the PSI for which the radiator cap is rated. Any additional pressure gets released to the coolant reservoir.

Pressurized Coolant Has a Higher Boiling Point

Automotive cooling systems are pressurized because non-pressurized coolant's boiling point is too low for effective cooling. To further raise its boiling point, automakers design cooling systems to hold pressure. When pressurized to 15 PSI, the boiling point of coolant is about 45 degrees Fahrenheit higher than non-pressurized coolant. As a result, it accommodates the engine's temperatures without turning to steam and evaporating.

The bottom line is that your vehicle's cooling system needs to be pressurized. Otherwise, the coolant will steam and evaporate. This can lead to serious problems such as overheating, blown head gasket, or a cracked engine. You could also experience a warped cylinder head.

How to Pressure Test Your Cooling System

You can see if your vehicle's cooling system is holding pressure by testing it. You’ll need a radiator pressure testing kit designed specifically for this purpose. Here is how to use it:

  1. Attach the system to the radiator where the radiator cap goes.
  2. Pump by hand until the gauge’s pressure matches the pressure written atop the radiator cap. (Most modern vehicles have a pressure between 13-16 PSI.)
  3. Let the vehicle sit with this pressure for 20-30 minutes.
  4. Inspect the entire cooling system for leaks.
  5. Check the gauge on the pressure tester for a change in pressure. If there is less than before, you probably have a leak.

After attaching the pressure tester, you should pressure test the radiator cap. Most radiator pressure testing kits come with an adapter to make this possible. Here is how to use it:

  1. Apply the adapter to the tester, then the radiator cap to the adapter.
  2. Pump by hand to the pressure indicated on the cap.

If your cooling system has any leaks, you should notice them rather quickly. If not, leave the pressure applied for a few minutes. If it doesn’t go down, then the cap is good. If the pressure does go down, it’s time to get a new cap.

JB Tools Has What You Need

We carry a variety of radiator pressure testing kits. You’ll also find radiator fillersradiator cap pliers, and radiator cleaners. These are just a small sample of the many automotive repair tools and accessories we stock. Shop JB Tools and get the lowest prices on what you need for your vehicle’s pressurized cooling system.