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4 julio, 2021


There is a frankly huge range of tests you can run to evaluate your car’s performance. It’s great that one of the most useful is also one of the easiest to do. We are talking about leak testing.

All you need to do one of these is some pretty rudimentary tools, a little knowledge, and some time to spare on a sunny afternoon. In this article, we take an in-depth look at leak testing. What they are, what they do and how to make one.

leak tester


Is a leak test a compression test? cylinder leak test

First things first and we have to address a common misconception here: a leak test is not a compression test. They are quite similar, so we understand why they can be confused with each other. But they are definitely different kinds of tests.

With a compression test, a pressure gauge is connected to the engine in place of the spark plugs. When the engine is started, the pressure gauge can measure this pressure. This is a compression test. It is a great indicator of the engine’s ability to generate pressure, which in turn is necessary to start and rotate the engine cylinder.

Poor pressure equates to a weak cylinder which, in use, will result in a low-performance engine that booms rather than roars.

What is a leak test? cylinder leak test

If it is a compression test, what is a leak test? Well, wait and we’ll tell you exactly what it is. Clever? A leak test is a compression test in reverse.

As we described earlier, a compression test is about measuring the pressure that the engine can generate on its own. A leak test also includes placing a pressure gauge on each cylinder of the engine, although in this case a leak test device is inserted, with a display incorporating two independent dials or displays.

It’s this dual dial display that really makes the leak test different from the compression test, but it also helps make it so useful. A pressure gauge measures the air pressure that the compressor introduces into the cylinder. The second dial tells you the percentage of air escaping from the cylinder (if any!)

So you can see that with a compression test, you are measuring the engine’s ability to generate pressure. With a leak test, you are measuring the engine’s ability to hold that pressure. Therefore, both tests are important ways of measuring engine health and performance, and they are also completely different.

How to perform a leak test? cylinder leak test

So we have discussed why you should perform a leak test. In the next section, we will see how to use and interpret the data that the test will generate. But before you can get to that stage, you need to know how to actually perform a leak test.

The first thing you’ll need to do is gather your gear! You’ll need:

  • A leak test tool
  • An air compressor
  • A socket wrench with a spark plug socket

The first thing you will need to do is remove the spark plugs from each cylinder with the socket wrench and spark plug socket.

For the leak test to work properly, you must first find top dead center for each cylinder before connecting the air compressor. To do this, you will need to remove the spark plugs as indicated above. When you remove them, insert something long and thin into the spark plug hole; a screwdriver will do the job. Start the engine by hand using a wrench on the crankshaft. When the screwdriver is at the point where it no longer rises or falls with each turn of the crankshaft, the cylinder is at top dead center.

Remove the screwdriver and hook the leak test tool into the spark plug hole. Put the car in gear if you can, but also set the parking brake so it doesn’t roll. Chocks behind the wheels can also be helpful.

When the leak test tool is connected to the cylinder, the next task is to connect the tool to the air compressor. Once the compressor hose is connected, turn the regulator clockwise to allow air to flow into the cylinder.

The dial on the right will give a reading as a percentage. This indicates the loss of pressure that is occurring (that is, the amount of air escaping from the cylinder). But more on that in a minute!

How to Read the Results of a Leak Test – Part 1 Engine Compression Leak Test

A leak test will give you two – yes, TWO – data sets. One is quite easy to interpret, while the other will require you to become something of an automotive detective.

The first set of results is right there in your hand, displayed on the dial …



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