Leak Detection: Smoke, Dye and Electronic Methods

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Leak Detection: Smoke, Dye and Electronic Methods

The average age of cars and light trucks on the road is now 11 ½ years, according to research from the latest Auto Care Association Factbook. Think about that for a moment. It means that you are dealing with higher mileage vehicles and  the issues that result for long-term wear and tear. Specifically, it means that fluid, coolant, vacuum and A/C systems are going to start leaking, causing problems. Finding the leak and fixing it can be challenging unless you have the right equipment and knowledge for the task. Let’s examine what you need to do this work.

Leaks come in many forms. Fluid leak-out can include coolant, lubricants, exhaust or refrigerants, but leak-ins can also occur, such as unmetered air in an intake system. The results can bring about different customer complaints, from overheating, dash lights, to being uncomfortable on a hot day, but the result is that at some point a technician is going to have to identify the leak and make a repair.

If it is a very obvious leak, for instance a blown upper radiator hose, a careful visual inspection is likely the only diagnostic needed to identify the concern followed by a straightforward repair. But that isn’t always the case anymore, and with the architecture of many newer engines requiring extensive disassembly to repair, making sure that you have properly identified the leak has never been more imperative.

Using a fluorescent dye for leak detection

Vehicles generally have a number of fluids involved in their proper function (coolant, engine oil, transmission fluid, refrigerant, etc.), and other than washer fluid and fuel (dyes are available for fuel leak detection) these fluids are contained in their own systems and not meant to be consumed or leak out.

As the engine ages, gaskets and seals degrade from the mechanical forces, movement, vibration, heat, corrosion and a number of other factors. Seals and gaskets are going to get hard and less flexible. Corrosion and wear are going to happen and this is eventually going to result in a leak.

The majority of engine leaks were easier to pinpoint in the past, and identifying the actual source of the leak was commonly straightforward. Yes, there were challenges, but since access was relatively generous, engines weren’t that complex, nor were they mounted sideways or covered in noise quieting plastic shields. But that isn’t the case anymore, as the under hood area is now crammed full and space is at a premium. Some form of disassembly is now going to be required to properly diagnose most leaks under the hood and pinpointing the actual source of the leak can be a complicated task.

Water pumps, for instance, are frequently mounted internally on today’s engines, with a weep hole in the timing cover. But this weep hole is usually hidden under an accessory, making it very difficult to identify the actual source of the leak. Is it the timing cover? Is it the head gasket? These leaks are not just frustrating, they are time consuming to properly diagnose, necessitating a method of leak detection that provides accurate results in a timely fashion, the first time.

One of the best ways to diagnose a fluid leak quickly and accurately is by adding a fluorescent dye into the leaking system.

The use of a fluorescent dye in combination with an ultraviolet (UV) or blue light inspection lamp is not new. The technology has been around for some time, but the dyes, and the lights used to identify the leak, have improved immensely.

There are now dyes that can be added to nearly all the fluids that could possible leak from a vehicle, even the air brake systems of heavy-duty trucks. Once the dye is added to the system, it has to be circulated with the fluid that is leaking.

And after circulation the leaking system has to be thoroughly inspected with the appropriate detection light to expose the leak that will need to be repaired.

Today’s detection lights are now offered in a vast number of handheld styles. Most use LEDs that are longer lasting, cooler operating, rechargeable and much safer than previous incandescent versions. They produce the UV or blue light required to make the dye glow brightly and come in a myriad of styles, shapes and designs. There are even lights available that are double ended and create both UV and blue light in one application.

The most vital part of using a leak detecting dye is using the correct light to detect it. This can’t be stressed enough. The use of poor quality dyes and improper UV or blue lights just won’t give the most accurate results and can lead to frustration for the technician. Using a UV light to find a leak on an AC system that has blue light dye installed might not show the leak’s origin.

Worse, the entire area being examined may glow and that’s not going to help identify the issue. Having both a UV and a blue light is your best bet in fluid leak detection, but attention to the dye’s instructions is imperative. There are now many dyes that are full-spectrum and compatible in many fluids (lowering cost and inventory) and glow when exposed to either style of detection light.

In addition, many manufactures are factory-installing dye in several of their fluids, cutting down on diagnostic time if there is a warranty issue. Careful inspection with your leak detection lights may reveal the area of concern before you add a dye into a system as you look for the source of the leak.

AC system dye has been a very popular leak detection method for years, and again most manufactures factory install dye in their AC systems. Carefully inspect first with your detection light/lights, even if the system is empty. If the system had dye in it before it lost its refrigerant, the florescent glow should remain at the source of the leak.

But if the system wasn’t factory dyed, a dye will have to be added. The AC dye is mixed into refrigerant oil to allow its installation in the vehicle’s AC system. The correct dye must be used: The oil that it is contained in has to be compatible with the AC system that you are dealing with. There are universal, dedicated PAG, Ester and R-1345yf/PAG oil dyes now available. Today’s AC systems hold very little refrigerant and refrigerant oil. They are very sensitive to an oil overcharge, so great care must be taken not to overfill the system.

Using a smoke machine

When dealing with a system that doesn’t have a fluid to transport a dye for leak detection, the smoke machine is an essential tool. Smoking out the leak in an evaporative system has been a mainstay for many years, and most of us have developed our own techniques. The EVAP smoke machine developed a low pressure, required to properly diagnose the EVAP system without doing any damage. This was mandated by the manufactures to allow testing, and many machines didn’t allow you to increase the testing pressure, all in the name of safety and the fact that the systems operated at such a low pressure during actual operation.

The same follows for intake leaks, and unmetered air entering the engine that can cause a variety of different engine codes. The naturally aspirated engine intake system operates under a vacuum or close to atmospheric pressure, but with the surge in turbo equipped engines, a different type of smoke machine is required.

The high pressure smoke machine is not designed to be used for EVAP diagnostics; it was designed to produce a pressure up to 20 psi, and be used to detect leaks and issues in the high pressure intake and exhaust systems of today’s popular forced induction engines.

The traditional low pressure smoke machine is not capable of simulating pressures in the intercoolers, turbos and ducting that may only leak when under a boost situation. If these systems leak, poor performance, noises, and engine trouble codes can be generated.

Boost codes and fuel trim codes can be created by leaks in the pressurized side of the intake system that will not show up in the service bay at idle because there is little turbo boost pressure.

But the intake side of the engine is not the only area that a high pressure smoke machine can be used. The exhaust side is susceptible to leaks as well and many of them go unnoticed. But an exhaust leak can cause a number of issues that are often misdiagnosed.

Catalytic codes P0420/P0430 are in the top 10 of OBD II codes generated year after year by today’s fleet, and many times a new catalytic convertor is installed, only to have the code return. When the powertrain control module (PCM) decides to perform a catalytic efficiency test, it is assuming that the exhaust system is sealed front to back, and calculates its decisions on this fact. But if there are any leaks, even small pin holes, the false air introduced will skew the readings of both air fuel and downstream O2 sensors and directly affect the PCM’s test results.

These leaks are often insignificant and don’t even create enough noise to alert the customer, but that doesn’t mean the PCM doesn’t see them. Pressurizing the exhaust system with a high pressure smoke machine will quickly tell you if you have any false air entering the exhaust system close to any of the air/fuel sensors or downstream O2 sensors. It will detect cracks, gasket leaks, broken bolt locations and weld failures that can allow fresh air to be sucked into the exhaust system and possibly cause a false converter code, when there is in fact nothing at all wrong with the convertor.

The high pressure smoke machine can also be used to diagnose cooling systems and wind and water leaks, something that a low pressure smoke machine just isn’t capable of doing.

Electronic leak detection

Electronic leak testers fall into two categories; electronic refrigerant testers and ultrasonic testers. The electronic refrigerant tester has been forced to evolve over the years to keep up with the types of refrigerant available. The introduction to R-1234yf is yet another part of the evolution that is going to take place.

Many of us already have an electronic leak detector of some description that we are using to check R-134a systems, but this detector may not work on the newer R-12134yf. Remember that R-1234yf is slightly flammable, so the proper detector is a must.

There are a number of new SAE performance standards for electronic refrigerant leak detectors and they are available at the SAE or MACS websites to make sure that your test equipment meets the current standards.

Many newer electronic testers now incorporate a dye detection UV/blue light on the sensor tip to aid in pinpointing the leak. The electronic refrigerant detector does have issues that the user needs to be aware of: The A/C system that you are leak testing must be charged with refrigerant for it to work, the detector has to be calibrated and properly serviced and they don’t like air movement over the sensor tip. The detection tips have a life span and wear out, filters have to be changed and most don’t like to have any air movement near the sensor head at all or false results will be indicated (for instance, don’t hold them in the vent duct with the fan on).

Following the operating manual and service procedures are paramount for accurate results.

Ultrasonic testers on the other hand are not susceptible to air movement and don’t require the system to have refrigerant in them to work, as the A/C system can be pressurized with an inert gas. The ultrasonic tester detects to the inaudible ultrasonic sounds that a leak creates, even in a loud noisy environment, but this tester isn’t limited only to A/C systems. It can also be used to find intake leaks, air leaks, exhaust leaks and vacuum leaks.

Choosing the leak detection method

Finding a leak is going to require an action plan, and that plan is going to depend on what type of leak you are dealing with.

Florescent dye fluid leak detection is accurate, easy and eliminates much of the guess-work in leak detection, making our job as techs more efficient, but the correct amount of dye has to be installed and the correct light has to be used for the ultimate results. The system being diagnosed will dictate the form of leak detection method you are going to use.

If you have a power steering fluid leak or a fuel smell, for example, the use a dye compound and detector light to find the issue is the best bet. If you have an A/C leak you are likely going to use a combination of methods (dye and electronic) making your diagnostics more precise. A P0420 is going to lead me to install a high pressure smoke machine to the tail pipe to check that there are no exhaust leaks that could cause a false code.

NOTE: The link below is to the SAE/MAC website and lists all the SAE requirements for A/C tools and equipment:    ■

Jeff Taylor boasts a 31-year career in the automotive industry with Eccles Auto Service in Dundas, Ontario, as a fully licensed professional lead technician. While continuing to be “on the bench” every day, Jeff is also heavily involved in government focus groups, serves as an accomplished technical writer and has competed in international diagnostic competitions as well as providing his expertise as an automotive technical instructor for a major aftermarket parts retailer.

To read more of Jeff Taylor's articles, see:

Brake System NVH Woes: Addressing and Avoiding Noise, Vibration and Harshness Issues

HFO 1234yf Refrigerant and Coolant Mapping

Some Diagnostics Hurt Your Brain: Fixing Difficult and Perplexing ProblemsMazda

Skyactiv Technology --What it Is, and What it Has Meant to Engine Packages

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