Vacuum, exhaust and fluid leak detection

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Vacuum, exhaust and fluid leak detection

Leon serves as one of the leading technical editors for Mitchell1. He is a graduate of Universal Technical Institute and has previously worked for Aamco Transmissions and as a mobile mechanic. He holds 609 Certification and specializes in automotive diagnostics.

In any service shop, a smoke machine is a great investment because of the variety of systems that it can be used to test. The use of smoke machines has proven to be an effective way to locate vacuum, exhaust, gas, oil and coolant leaks. They are also easy to use: simply plug in and turn on. The machines produce a thick white smoke with pressure around 1 psi to 2 psi. The smoke then spreads throughout the system being tested. If there is a leak, smoke will become visible. Using a bright flashlight helps in locating the smoke, especially in dark, cramped areas of the engine bay.

Vacuum, exhaust and gas leaks

Vacuum, exhaust, and gas leaks have proven to be difficult to diagnose due to the leak often being a small hole or crack, thus a smoke machine proves to be very effective.

Smoke machines typically take around one to two minutes to fill the engine and spread throughout, then it’s a matter of spotting were the smoke is leaking from. Small things like a bad gas cap could be the cause of a gas leak, so check the car thoroughly.

1. With the engine off remove the vacuum hose from the PCV valve and pump in the smoke using the PCV vacuum hose. If the
PCV valve isn’t in reach, pumping smoke into the brake booster vacuum hose also works.

2. Check automobile for leaking smoke.

Coolant and oil leaks

Finding a leak with a pressure gauge is one way to test the cooling system, but unless you can see the leak it is not very useful.

Using a smoke machine will allow you to visually see the exact location of the leak. This is also a great way to pinpoint an oil leak without second guessing if you found the source of the leak.

The system should be full after about one minute of pumping smoke, so if there is a leak present it should be visible.

1. To find a coolant leak using a smoke machine you must drain the coolant from the system, then pump smoke into the radiator and look for a leak.

2. Before testing for an oil leak you first must disconnect and pinch the PCV hose so smoke does not leak back into the intake, then seal the crankcase with a piece of tape.

3. Pull the dipstick and pump the smoke into the oil dipstick tube and wait for the smoke to become visible.


Intercooler and turbocharger

Having a turbocharged or supercharged engine is great, but it is extremely important to keep the engine running cool to prevent mechanical damage. For turbocharged systems to operate efficiently there can be no leaks in the turbo itself, ducting, exhaust or the intercooler. Engine compartments with turbochargers run hotter than those without them due to the excessive speeds at which a turbo operates. The heat causes hoses and seals to dry out and leak. The use of a smoke machine helps in detecting leaks to prevent engine and turbo damage. A turbo system consists of two different sides: the cold side (intake) and the hot side (exhaust).

1. Hot side: Pump smoke into the exhaust pipe using an exhaust cone, then inspect the exhaust manifold and exhaust for leaks.

2. Cold side: Pump the smoke in to the intake system, with the intake under smoke pressure, the intercooler, the ducting, the waste gate, and the “cold” side of the turbo can be inspected for leaks.

Air and water leakage

People tend to forget that window seals are parts that also require maintenance so they won’t dry out. If your customer complains that he was in a drive-thru car wash and felt water dripping on him, or that he hears a whistling noise while driving down the highway, chances are his vehicle’s window seal in dried out. Thus the use of a smoke machine is an easy way to detect if there is a leak in the window seals.

1. Turn on the vehicles A/C to high and set to outside air (creates cabin pressure).

2. Connect the smoke diffuser to the smoke machine hose.

3. Pump the smoke along the window seals (if there is a leak you will see the smoke being redirected).

A/C diagnosis

Summer is approaching faster than we realize, and when it comes to the A/C system no one ever wants to wonder if their A/C is going to cool. Most A/C systems contain 2.5% to 3.5% air in the refrigerant for normal operation and as little as 2% air in refrigerant can cause problems.

There are several ways to detect an A/C leak including the use of soapy water, UV dye leak detection, and several ways of electronic leak detection. Most serviced A/C units are found to be leaking refrigerant due to malfunctioning parts. Most leaks are found at connections in the system and sometimes tightening the connections can eliminate a leak, if the O-ring is damaged tightening the connection will not stop the leak and O-rings will need to be replaced.



Soapy water

Using soapy water is an easy way to test to see if there is an A/C leak in the car, although soapy water is only good for detecting leaks over 40 ounces a year. To make the soapy water effective make sure that it’s a thick mix so the leak will show better. You also will need a brush.

1. Start by getting the soapy water and brushing it over the entire hose fittings and the A/C service ports, not having caps on the service ports can also lead to a small leak.

2. Start the engine and turn on the A/C to high and watch to see if the soapy water starts to bubble. If it does bubble that indicates that there is a leak.

UV dye

Another method of finding A/C leaks is with the use of an ultraviolet light and a fluorescent dye. Some manufacturers, like Chevy and Ford, have dye standard in their systems, making it easier to detect a leak. For systems without dye it can be injected into the refrigerant. There are many different types of dyes, so make sure you follow the manufacturer’s instructions. Some manufacturers don’t recommend dyes in their system, and in some cases it can void factory warranty if found. This method is effective because it can locate leaks that only occur while the vehicle is being driven. Technicians are big fans of this test because they can show the customer where the leaks are in their car. A downside to this testing is that it is difficult to detect an evaporator leak.

1. Wearing special UV glasses, scan the system using the black light.

2. If there is a leak you will see a “nuclear green” slime type color.

Electronic leak detection

There are three types of electronic leak detection. Infrared sensors are the most sensitive, ultrasonic detectors listen for sound (gas leaks) while the user wears headphones, and the heated diode or heated triode is said to be the best. These devices work by detecting the sound of leaking gas, hard to do if not in a quiet area. The best way to test the system is while the engine is still cold. Depending on the specific system, this method may or may not be as effective in exactly pinpointing the leak.

1. Move the probe about 2 inches per second along the A/C system while keeping a distance of 1/2 inch.

2. If the probe detects a leak it will start clicking or lighting up and as it gets closer to the leak it will click or light more and more rapidly.

Technologically advanced ultrasonic testers convert and amplify inaudible ultrasonic sound into “natural” sound. This enables the technician to “hear” sounds that signify problems such as air brake leaks, compressed air leaks, vacuum leaks, tire leaks, EVAP system leaks, and more. To cite but one example, Tracer’s Tracerline Marksman II reportedly is so sensitive that it can detect a leak from orifices as small as 0.004 in. at 5.0 psi, from a distance of as much as 12 in. A 5-LED signal-intensity indicator and audible alarm pinpoints the leak source. According to Tracer, an internal noise control feature buffers ambient noise, making the tool usable in noisy environments.

For an example of smoke machine features and use, refer to our January/February 2012 issue (review of the Smoke Wizard GLD-50).



Leak detection equipment suppliers


Clore Automotive,

Global Leak Detection (Smoke Wizard),

Mac Tools,


Matco Tools,

MotorVac Technologies,

Myers Tire Supply,

Redline Detection (Smoke Pro),


RTI Technologies,

Snap-on Tools,

SPX Corp.,

Star EnviroTech,

Streamlight, www.streamlight,com


U-View Ultraviolet Systems,

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