Lessons on leak detection

Cappert discusses questions about leak detection products


A. Electronic vacuum leak detectors find leaks using ultrasonic technology. That is, they “listen” for the high-frequency characteristics that vacuum leaks produce, outside the spectrum of human auditory detection. Leak detectors with this type of technology produce an audible and visual indication when you're near a leak with the detector's probe. This sure beats trying to find a leak by sound, since you're typically trying to pinpoint a leak with the noise of the engine in the background. So yes, ultrasonic detectors can be extremely effective when chasing down vacuum leaks.

Q. We perform a lot of brake diagnostics and one of my techs asked about using dyes to detect hydraulic leaks. Do they work for this application?

A. Exercise caution here as dye-based leak detection technology is generally not intended for braking systems. For the most part, dye-based detectors usually work only in circulating systems. In other words, dyes typically work on systems where oil, coolant, refrigerant or other liquids or gases are continuously being circulated in a “loop.” With that said, new products are always emerging in the market, so always check with the manufacturer to see if they explicitly state their dye system can be used on automotive hydraulic braking systems.

Q. How do I know the refrigerant leak detector I'm considering is up to par with industry requirements?

A. If you're considering an electronic leak detector for R-134a systems, make sure it meets the minimum performance criteria spelled out in SAE J2791. Labeling on the detector should clearly state that the product meets the requirements of this standard. If there's any question, check with the manufacturer. Remember, the sensitivity of detectors meeting this standard work hand-in-hand with an established procedural standard for using the detector, SAE J1628. Similar guidance comes into play when choosing a dye-based detector. When looking for one of these, look for dyes that meet SAE standard J2297, and remember to affix a label to the system stating that a dye has been added. As with electronic detectors, using a compliant dye-based system works in concert with another SAE procedural standard, J2298.

Q. When using a dye-based detector for finding oil leaks, how long do I need to wait after adding the dye to the system before I begin checking for leaks?

A. After adding the dye to the engine, just allow it to circulate a few minutes with the engine running and you can begin searching for the leak right away. Remember that the ability to detect the leak will depend on the rate of the leak, and the amount of time that the dye circulates. Some leaks will be readily apparent in a short amount of time; others may take more time.

Q. After I've added dye to a system for leak detection, do I need to flush the system once repairs have been made?

A. No, approved dyes can remain in the system after a leak is fixed and will cause no harm. In fact, the dye still in the system can be used to verify repairs afterward. Always use dyes at the recommended ratio for the system they're being used in.

Q. We specialize in exhaust systems and frequently check for exhaust leaks during diagnosis. Our usual technique involves restricting the exhaust at the tailpipe and then listen for leaks. Is there a more effective way to look for exhaust leaks?

A. Yes, a smoke machine provides a simple and effective means of pinpointing exhaust leaks. Using an adapter cone at the tailpipe, you activate the smoke machine so that it fills the exhaust with smoke, Then, inspect all potential leaks points for escaping smoke, including pipe connections, manifold flanges, and others.

Q. Our collision shop faces leaks from sunroofs and general wind and water leaks from doors and windows. Any tips for taking some of the guesswork out of finding these problems?

A. A smoke machine or ultrasonic leak detector can help you pinpoint problems in these areas, possibly eliminating the need to drive the car or spray suspect areas with a hose. Simply apply smoke or pass the ultrasonic leak detector's probe near suspected leak points to find leaks in a lot less time.

Q. We use a dye-based detection system in our shop for finding coolant leaks, but it sometimes takes several attempts to find leaks. Is there anything we can do to improve our odds when isolating these types of leaks?

A. Yes, to help with your success, also use a cooling system pressure tester to emulate the pressures found in an operating cooling system. This may help push coolant out of weak spots in the cooling system, thus increasing the odds of finding a leak the first time out.

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