build and use a leakdown tester (2024)

FAQs

How to properly do 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.

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.

The difference in readings gives you the percentage leak-down. You'll need to prevent the crankshaft from turning, resisting 100 pounds per square inch normally used to test automotive gasoline engines. Diesel engines are typically tested at 200 psi. Small two-cycle and four-cycle engines might need only 50 psi.

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.

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.

What is the limit for a leak test? ›

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).

Leak-down tests cylinder leakage paths. Leak-down primarily tests pistons and rings, seated valve sealing, and the head gasket. Leak-down will not show valve timing and movement problems, or piston movement related sealing problems. Any test should include both compression and leak-down.

Ultrasonic Testing

As a gas flows out of a larger leak, it can generate Ultrasound. This can be detected with ultrasonic microphones. There is also a variation of this in which an ultrasound emitter is placed inside a sealed volume. Both these techniques are used to locate leakage.

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.

The difference in readings gives you the percentage leak-down. You'll need to prevent the crankshaft from turning, resisting 100 pounds per square inch normally used to test automotive gasoline engines. Diesel engines are typically tested at 200 psi. Small two-cycle and four-cycle engines might need only 50 psi.

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.