In the video above, veteran mechanic Scotty Kilmer demonstrates an easy, inexpensive method of finding a vacuum leak in a car’s engine. Automotive repair is one of the most popular and common reasons for vacuum leak testing, and automakers and DIYers all over the world use a range of testing methods to make sure they’re getting the most out of their automobiles.
However, vacuum leak testing is important for much more than just automotive maintenance—equipment and devices used in a broad range of industries require vacuum testing to ensure proper construction and performance.
Some Technical Considerations
As Kilmer shows, vacuum leak testing is actually a relatively simple process in theory. But, if you need specific, quantifiable, repeatable information, you need more than a cheap cigar and a length of rubber tubing.
Accurate, measurable vacuum testing of an automotive engine, for example, is a far more involved process. A tachometer and vacuum gauge are required for this process, as is a working knowledge of the engine itself. One must be able to identify and disconnect/reconnect a non-regulated vacuum source and fuel vapor canister vacuum lines, among other things. Reading the vacuum gauge with the engine idling, and comparing those readings to the engine at 2000 RPM, can reveal any of a number of problems:
- A vacuum reading below 18 Hg at idle indicates inadequate vacuum.
- Fluctuating vacuum readings at idle may indicate sticking and/or leaking valves, and/or a misfiring ignition.
- Readings that fluctuate at idle but remain steady as RPMs increase may indicate leaking valves or a faulty camshaft.
- Vacuum readings that fluctuate more as RPM increase may indicate a faulty head gasket, leaking valves, weak or broken valve springs, or a misfiring ignition.
- If vacuum gauge readings fluctuate regularly with each engine cycle, a burnt or leaking valve or improper valve clearance may be the problem.
- Readings that drop steadily as RPMs increase can indicate excessive back pressure due to restriction in the exhaust system or catalytic converter.
- Vacuum gauge readings that drift slowly at idle may indicate an overly lean air/fuel mixture or a minor vacuum leak.
- If the vacuum reading remains steady between 18 Hg and 22 Hg, the engine’s vacuum system is likely in good operating condition.
Vacuum Leak Testing Equipment
As indicated by the numerous possibilities listed above, the information gleaned from vacuum leak testing can be extensive and widely varied. As such, it is preferable to use the proper equipment to conduct this type of testing.
There are a wide range of “standard” leak testing devices available from countless manufacturers. Model may be uniquely designed for testing specific equipment, or may be more general testers that can be used in a variety of applications. Certain manufacturers produce custom leak test systems that can be modified to meet the specific requirements of the product to be tested or the testing process that must be performed.
• ScottyKilmer.com http://www.scottykilmer.com/
• “Finding Engine Vacuum Leaks With A Cigar” https://www.youtube.com/watch?v=zMok2y05jNE
• “How to: VACUUM TESTING” http://www.austincc.edu/wkibbe/vacuumtesting.pdf
• Vacuum Leak Testing Systems http://www.cincinnati-test.com/custom-engineered-systems-vacuum-leak-test-systems-c-1_44_153-l-en.html