Doing a cylinder leak down test can tell you more about your engine than you think. The cylinder leak down test reading is expressed in a percentage.
2007 Sti Oil Consumption Compression Leakdown Test Results
Cylinder leak down test acceptable result. In simplified terms if air is pumped into the cylinder at 100 psi and the gauge reads 97 psi then the leak down percentage is 3. So a compression test measures how well your engines cylinders are sealing. How you roll the engine over to tdc will also have an effect on leakdown do not back up the crank and dont go even slightly. It does little good to measure leakage with the piston at. No engine will have perfect sealing with 0 percent loss. Five to 10 percent loss indicates an engine in great to good running order.
Above 20 percent loss and it may be time for a teardown and rebuild. Then using a similar type of connector as the compression test we fill the cylinder with pressure. Cylinder leak down is a great tool to diagnose problems but if the engine doesnt have any problems other than what you are testing for id let it go and drive the thing until it is completely broke in. Doing a leak down test is a fairly simple matter. The way to get to the final answer for a given test is. A leakdown tester can point out problems that a compression test wont.
Lets say that they were all within 10 percent of each other in pressure with a peak of around 150 to 170 psi. The intake valve leads to the intake manifold and the exhaust valve leads to the exhaust tailpipe. The tester then measures the volume of air needed to maintain a predetermined pressure in the cylinder. This is done by inserting compressed air around 100 psi into the cylinder at tdc and then measuring how much is lost from the seals. The leakdown test measures how well the cylinder is sealing. The tester is connected to an air source and is attached to the engine through the spark plug hole.
You didnt mention whether there were a couple of cylinders that were greater than 50 60 percent. For example after you connect the 80 psi static pressurized tester to the engine the left side regulator controlled gauge may say something like 70 psi after it drops while the right side engine leakage gauge may say something like 65 psi. Always make sure to test cylinder leakage with the piston at the top of the cylinder. Also a cylinder leak down test can pinpoint issues in specific areas that other tests can not. This is where the greatest cylinder wear occurs. A cylinder leak down or cylinder leakage test is actually similar to a compression test.
Consequently good cylinder leakdown readings should be below 5 8. An engine between 10 and 20 percent can still run ok but itll be time to keep an eye or ear on things. Perform a cylinder leakage test by injecting regulated shop air into the cylinder heads spark plug hole then visually searching and listening for a leak. The valves rings and head gasket seal the combustion chamber. First i would run a compression test looking for weak cylinders.
Gallery of Cylinder Leak Down Test Acceptable Result
