Conducting a smoke test is a great way to diagnose whether your vehicle’s intake system has leaks.
Even though this method is used primarily for intake systems, smoke tests can also be used to find leaks in a vehicle’s evaporative emissions system or exhaust system.
Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.
Pro Tip: This was the original reason for smoke machines, since EVAP system leaks can be so hard to locate. On OBD2 vehicles, EVAP leaks will store codes and trigger the check engine light.
What Is a Smoke Test on a Car?
A smoke test is a procedure that’s done to your vehicle’s intake system to check for any leaks. This test involves using a smoke test machine that uses a special fluid similar to baby oil to create smoke and gently pump it into the engine’s intake or vacuum hoses so that the positive pressure in the cavity or hose will exit through a leak point. The better smoke fluid will have ultraviolet dye to assist with finding the leak even if the smoke is barely visible.
Most smoke tests keep smoke at a moderate level so that it doesn’t damage the engine. The smoke producing fluid doesn’t produce toxic smoke; it smells like lemons. Baby oil smoke is a bit more toxic than smoke fluid smoke.
The smoke producing fluid used in a smoke test doesn’t produce toxic smoke; it smells like lemons. Baby oil smoke is a bit more toxic than smoke fluid smoke.
– Richard McCuistian, ASE Certified Master Automobile Technician
Why Is a Smoke Test Necessary?
Smoke tests are necessary if you want to find small and hidden leaks. Large leaks in the intake system can create whooshing noises, which can be found without requiring a smoke test. However, vacuum leak testing with smoke makes finding small leaks easy. If you suspect a vacuum leak, allow some smoke to drift in the area of the leak and you may see it draw in.
Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.
Pro Tip: If a vehicle has wind noise, you can close all the doors, put the A/C on “norm” to draw outside air in, and turn the blower motor on high while passing the smoke nozzle along next to the door joints and windows. The positive pressure you’re creating in the car with the blower motor will leak out past the door seal where it’s leaking and disturb the smoke stream.
For the most part, a small leak is a minor issue and won’t cause major drivability issues. These small leaks can trigger an illuminated check engine light and a stored trouble code in your vehicle’s diagnostic system, as the mass air flow sensor can detect the extra or lackluster airflow. Small air leaks can cause your vehicle to have lackluster boost pressure or have a lean running engine.
These small leaks might not mean much, but they can make a difference if you intend to race your vehicle on the track and you want the most performance.
More About Leaks
The low pressure created by the action of the pistons and valves draws atmosphere into the intake plenum. The pressure in the intake is always lower than atmospheric pressure unless the engine is supercharged or turbocharged.
This tightly controlled airflow through the plenum into the cylinders is vital for a smooth idle, combustion, and power production.
In some vehicles, there’s a turbocharger (driven by exhaust flow) or a supercharger driven by a gear or belt to draw atmosphere in, compress it, and then push the air into the intake plenum, creating a positive pressure that is higher than atmospheric pressure for increased volumetric efficiency beyond what the engine would have without the forced induction.
Some turbocharged or supercharged engines have an intercooler, which is basically a radiator that cools the compressed and heated air before it enters the plenum.
A leak in the engine’s intake system disrupts the air/fuel mixture, particularly at idle. A vacuum leak of this sort is typically more noticeable at idle than it is when driving.
On MAF equipped engines, this is known as an “unmetered air leak” and will cause the PCM to add fuel, increasing fuel trim to keep the O2 sensors switching and the catalytic converter happy.
How To Conduct a Smoke Test
Conducting a smoke test involves using a smoke generator designed for automotive testing. There are high-tech diagnostic smoke machines where you can control the amount of smoke and air pressure. There are also makeshift smoke machines that use glass jars, hoses, soldering iron, rags, and baby oil. These smoke machines use a soldering iron to burn baby oil in the glass jar. There are a lot of online videos on how to make a homemade smoke machine.
In a smoke test, plastic tubing funnels the heated and smoky air into the engine’s intake manifold, evaporative emissions system, or even exhaust system.
An easy path for the smoke to enter the intake system is through the positive crankcase ventilation (PCV) vacuum hose, which hooks up to the intake manifold. Once the smoke generator is pumping smoke into the system, you should try to find where the smoke is leaking. Using a powerful light is going to help make any small leaks more visible. You should continue pumping air into the channels for about thirty minutes to ensure the smoke gets into all the nooks and crannies.
How Much Is a Car Smoke Test?
The cost of conducting a smoke test in an auto repair shop will be around $50 to $150. The cost might increase if you’re conducting a smoke test on several vehicle systems.
If the smoke test reveals a problem, then you likely need to spend more to resolve the issue. This might require purchasing new components and spending on labor.
If you conduct the smoke test yourself using a homemade smoke machine, then you’ll likely end up spending only a fraction of the cost.
When Do You Need To Conduct a Car Smoke Test?
When to do a smoke test on a car? A smoke test can be considered if your vehicle is showing these symptoms:
- A rough idle
- A hissing sound from the engine bay when the vehicle is running
- A higher idle RPM
- An illuminated check engine light
- Increased fuel consumption
- Reduced power and ability to accelerate
A minor air leak in the intake manifold isn’t a major issue, although it will affect fuel trims at idle. However, if this small leak is allowed to persist, it can worsen. When this happens, the engine might have trouble idling and can stall.
As much as possible, you should seek a professional when diagnosing and fixing issues since they’ll be equipped with the right tools needed for a smoke test. Additionally, they’ll have the right skills to fix any issue they might find.
Get a New Intake Manifold From the Comfort of Your Home
If the smoke test uncovers a leak in the intake manifold, fix it as early as possible. That minor leak might get worse if left to its own devices, leading to more problems and costlier repairs down the line. Luckily, you can order a replacement intake manifold from CarParts.com without leaving your home.
CarParts.com offers fast and secure online shopping on your mobile device. We make it easy to find the right intake manifold for your car or truck. Plug your vehicle’s year, make, model and engine in our website’s built-in vehicle selector to bring up the best results. You don’t have to wait long for the part, either. Our distribution centers are strategically located to ship on-hand parts to your address quickly and safely. You can expect your new intake manifold to arrive within several business days if you live within the continental US and complete your order before noon ET.
So, what are you waiting for? Visit CarParts.com and order a new intake manifold for your vehicle that delivers the best bang for your buck!
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