build and use a leakdown tester (2024)

FAQs

What are the good numbers on a leak-down test? ›

No engine will have perfect sealing with 0 percent loss. Five to 10 percent loss indicates an engine in great to good running order. An engine between 10 and 20 percent can still run OK, but it'll be time to keep an eye (or ear) on things. Above 20 percent loss and it may be time for a teardown and rebuild.

For normally aspirated engines, 5 to 10 percent loss indicates the engine in great condition. If an engine reads between 15-20 percent, it's not a reason for condemning the engine – but be more concerned about where the leakage is occurring. And at 30 percent, there are some major problems and an overhaul is likely.

The concept is simple. Pump air at a known pressure into a top-dead-center combustion chamber, then measure how much pressure the chamber holds. The difference in readings gives you the percentage leak-down.

How to Calculate Leak Rate (SCCM) A leak rate is expressed as a volume per unit of time. The rate is found by measuring the change in pressure multiplied by the volume. That number is then divided by the change in time multiplied by the surrounding atmospheric pressure to calculate the leak rate (SCCM).

Cylinder Leak Down Test Results

So if you test an engine and see leakage numbers even in the 15 to 20 percent range, this is not cause for alarm. Much of your concern around an engine that needs freshening should revolve around exactly where the leakage originates.

Heating appliances should have a current that should be less than 0.75 milliamps per Kilowatt up to a max of 5 milliamps. Portable/handheld appliances have to have earth leakage current of less than 0.75mA to be considered safe.

Again, a good rule of thumb is no more than 10 percent variation between any of the cylinders.

A leak-down tester may represent a larger initial investment, and a leak-down test takes more time to perform, but it can give you a more accurate and detailed picture of the engine's overall health.

Method to perform a leak test by placing the work in a chamber, applying a minute amount of pressure inside the chamber, applying test pressure inside the work and comparing the pressure change due to leak from the work to chamber with that of the master work.

The leak test pressure limit for leak tests typically uses low pressure. Most codes for leak test pressure limits call for the pressure to be at least 15 psi or 25% of the design pressure (whichever pressure is less).

What pressure is a leak down test? ›

The input pressure is set for 80 psi (550 kPa), and 60 psi (410 kPa) minimum cylinder pressure is the accepted standard. While the leak-down tester pressurizes the cylinder, the mechanic can listen to various parts to determine where any leak may originate.

Test results shall be acceptable if there is no visible leakage during the hold period. Pressure shall not vary from the test pressure at the start of the test by more than 5 % or 500 psi (3.45 MPa), whichever is less, during the entire hold period, and shall not drop below the test pressure.

A leak rate of 10^-12 mbar · l/s corresponds to hole diameter of 1 Å; this is the lower detection limit for modern helium leak detectors.

Test air leakage rate:

With a fully-charged air system (typically 125 psi), turn off the engine, release the parking brake, and time the air pressure drop. The loss rate should be less than 2 psi in 1 minute for single vehicles and less than 3 psi in 1 minute for combination vehicles.

There are also single-gauge leak down testers. These gauges require you to zero the gauge with reference air (usually at 80 psi or below) before connecting the output line to the cylinder. Zero the gauge with the regulator. Once connected to the cylinder, the gauge will read out the actual cylinder leak rate.

At a local home improvement store, a smoke pencil should only cost around $30 and is a great way to know how to check air ducts for leaks. Using the device, slowly move it over your ductwork to see if there are any movements inside of your ductwork.