Performing An Engine Leak Down Test
January 27th, 2010 Muscle CarsPerforming An Engine Leak Down Test
The performance of your car’s engine is dependent on the air and fuel that is drawn into each of the combustion chambers during operation. When air and fuel enter a chamber, the intake and exhaust valves close, sealing both inside. Within the chamber sits a piston. It rises and compresses the air-fuel mixture. A spark plug sits atop the chamber and ignites the compressed mix. The resulting explosion forces the piston down and ultimately is responsible for propelling your vehicle forward.
If the pressure within the combustion chamber declines due to leakage, misfires and similar problems can occur. That will hamper your engine’s performance. A leak down test measures pressure loss within the cylinders. A mechanic will often use this test to identify whether a leak exists as well as its root cause.
Below, you’ll learn how a leakdown is performed and some of the potential problems it can help to identify. If you have the proper gauge, you can do the test at home. Otherwise, an auto technician can do it for you.
How The Test Is Done
First, you’ll need to remove your spark plugs. You’ll then need to position each cylinder’s piston at top center of its chamber. Second, connect the coupling on your leakage gauge to the hole in which your spark plug usually rests. Third, fill the chamber with compressed air and take a reading on the leakage percentage.
It’s important to realize that there will always be some measure of leakage from each of the chambers. If the gauge shows less than 10%, your engine is fine. If the leakage percentage is between 10% and 20%, it’s still in good condition, but you’ll want to note any changes in its performance. If the gauge shows 30% or more, you have an engine problem.
Identifying Potential Problems
One of the advantages of a leakdown test over a compression test is that it’s easier to identify where the lost pressure is headed. This is important if fixing a leakage requires taking apart your engine.
For example, if you hear air leaking out of your car’s tailpipe, the problem is likely your exhaust valve. On the other hand, you might notice a whistling sound coming from your intake; that signals a leak in your intake valve. Hissing from your PCV valve suggests the piston rings are failing.
If you look at the top of your radiator reservoir (take the cap off) and see bubbles, it could mean a leakage problem with your head gasket.
As noted, a leakdown test is easy to perform at home. You’ll need a leak down gauge, a source for the air that you’ll send into each cylinder’s chamber, and a few tools (e.g. a socket to remove the spark plugs). Armed with those resources and a little free time, you can perform a leakdown to find the root cause of a pressure loss.
Tags: Car Care, Car Engine, Car Maintenance, Car Tips