4 steps to take DIY leak down test

The term “leak down” is also known as the “loss reading”. It refers to the amount of compression that’s lost by the engine measured in percentage units. In other terms, this test is called the Cylinder Leakage Test. This is similar to a compression test and even the steps to do it are almost the same.

The two tests require the usage of tester hoses that come with each respective testing kit. However, in a leak down test, you are looking for opposite of the result of a compression test.

The leak down test uses a store-bought leak down tester with two gauges. It also requires a good source of compressed air. One of the two gauges on the leak down tester is for monitoring the pressure while the cylinder of the chosen vehicle is being pressurized.

The other gauge shows what you are after – the pressure that is lost through a leakage measured in percentage. To better understand leak down test, read on this article from Philkotse.com. We also provided the step-by-step process of leak down testing. 

1. What is a “Leak Down Test” for?

A leak down test is a kind of like a regular check-up for your car. It will help you detect problems that may be present in your vehicle’s cylinder which can be affecting its mechanical health. Similar to illness in humans, you would also need to do this early in the stage of the problem or as a maintenance procedure to detect early signs of damage.

Mechanics usually do this when vehicle owners suspect that something is wrong with their car’s engine.

When the leak down test is performed, compressed air helps the person identify where the leaks could be – or if there are any leaks at all. Once the leaks are identified, it will be easier for the owner or the mechanic to think of the succeeding steps to remediate the damages.

The leak-down test will help detect problems that may be present in the vehicle’s cylinder

2. Before doing the leak down test

Before performing the leak down test, you first have to make sure that your car engine is at its Top Dead Center or also referred to as TDC. By doing this, you are making sure that there is no other way for any compressed air to escape. Putting your engine to its TDC means that the piston should be at the summit of its travel.

Both the intake and exhaust valves should also be closed to make sure no air escapes. To get your engine to TDC, you would have to literally use your hands to turn the engine over. This is easy to do if you first remove all the spark plugs connected to it.

Make sure that your car engine is at its Top Dead Center or also referred to as TDC

Also, make sure that the vacuum gauge that came with your tester kit can measure and vacuum. While rotating the engine, look for the gauge and let it go into positive. As the piston gets closer to its TDC, the pressure should go to zero.

Remember that it will vacuum back up as it passes TDC and then back again. This process goes back and forth so you should time your gauge exactly when TDC happens.

Make sure that the vacuum gauge that came with your tester kit can measure and vacuum

3. How to do a leak down test

Once you’re sure that your car is at its Top Dead Center, you can now proceed to take the leak down test. Note that since most of the important part will be done by a piece of machinery, you would need to purchase a brand that you trust. The leak down tester that you choose for the job should give you accurate results. It is recommended to go to Banawe street to find the best deals on car accessories.

If not, it may give you a false reading and you may respond adversely to what your car really needs. Pick a brand with a good reputation and stay away from those that are tagged with prices that are “too good to be true”. You can always trust your instincts when you’re buying the tester personally.

However, it also won’t hurt if you ask the sales attendant for some advice.

You should purchase a brand that you trust

If you’re happy with the leak down tester you’ve selected, you can now proceed to the next steps.

Step #1: Attaching the leak down tester to your sparkplug

After securing the cylinder to TDC, hook up the leak down test tool onto the hole of your car’s sparkplug. If you can or you have an available buddy around who can help you, ask them to put the car in gear.

After securing the cylinder to TDC, hook up the leak down test tool onto the hole of your car’s sparkplug

Also, ask him to engage the parking brake to prevent your car from rolling away. Using some triangular chunks of wood to hold the rear wheels in place also help secure your car in place. If that’s not available, bricks or chunky rocks can also do the trick.

Step #2: Attaching the leak down tester to the cylinder

You would now need to attach the testing tool to the air compressor. After securely connecting the compressor hose to your tool, take the regulator and turn the gauge knob clockwise. This will now start allowing the air to flow straight into the cylinder.

Step #3: Getting the results

 We explained earlier the use of the two gauges. For the results, you would have to look at the gauge at the right-hand side. This will indicate the amount of air that your engine losses measured in percentage.

Best way to perform a cylinder leakage test

>>> More car engine maintenance tips: 

• 5 simple tips to maximum your car engine's performance
• 4 Essential Care Tips for Maintaining Your Car Engine

Step #4: Understanding the results

The result of the test in the right-hand gauge will be easy to read because the results are measured in a 0-100% range. Below we have different percentages and readings. You can refer the results of your test to its corresponding meaning.

With 1%-10%, it means everything is good and you should have nothing to worry about.

If the range is between 10%-20%, there will be pressure loss but your engine will most likely be fine. There will also be minor changes when it comes to your vehicle’s performance that can affect acceleration, fuel economy and the likes. Know that this may get worse over time if not addressed immediately.

When it shows the result of 30% and higher – This type of reading means that your engine is suffering. It can get you in trouble at any given time the moment that you use your vehicle. Get your vehicle to an auto repair shop as soon as you can to get the leaks remediated.

30% and higher is the figure alarms you have your car repaired by an auto shop as soon as possible

You can watch the video below to have a more general look at how to take the leak down test.

Stay tuned and we will update more information for you on our tips and advice.