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Answering All Your Car Questions

What are leak down test for?

By Jakob Jelling

A leak down test is a kind of compression test which allows measuring the ability of the cylinder to hold compression. It is usually done in combination with a compression measurement and together they provide very important information regarding the car engine and help diagnose problems in that car area.

The test which allows car owners to learn about the ability of the cylinder to hold compression is what is known as the leak down test and works by measuring the pressure in a hot engine. This test is done by supplying air and checking the compression through the pressure measure.

There are specific tools used in order to apply leak down tests which differ to the tools used for basic compression tests called compression testers. These basic compression testers are pressure gauges which must be used while the engine is warm in order to properly measure the maximum compression pressure. Once you learn this value you can compare it with the ideal one indicated in the car owner's manual.

If the compression pressure is too high, this probably indicates that there is a problem in the combustion chamber. On the other hand, if the compression pressure is too low, this surely means there is a problem and you should look where its root is since there can be many different failures causing it.

The leak down testing tool checks if the cylinder can hold any specific amount of compression without problems. Besides this, it allows you to find out where the compression leak is allowing you therefore to look for a way of fixing it. Besides this, you can find if the cylinder has any defect as well as you can also learn where is the exact point in which pressurized air escapes by listening while applying the test.

Through the application of the leak down test and depending on where you hear the air escaping from you will be able to determine what exactly is going on and fix it accordingly. This way, a leak down tester usually provides much more useful and complete information than the one which a compression gauge would.