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Use a Smoke Machine to Find Engine Vacuum and Other Leaks

Fluid leaks are usually easy to find. Just look for the drips. Vacuum leaks are not so simple. If the leak is massive, then you can usually hear it or use a propane enrichment tool to locate the spot (the engine speed will increase and smooth out).

If the leak is small or in an awkward place, the propane enrichment method (or carburetor cleaner spray method) is inconclusive. What if you are looking for a reason the engine in your combine is not building maximum turbocharger boost or your vacuum meter planter is not working consistently? The answer is to use a smoke machine.

This apparatus allows the introduction of a nonflammable smoke into a component, quickly revealing the leak(s). Just follow the smoke.

On an engine (gas or diesel) there are many connections, grommets, seals, lines, and tubes in the induction system, and they are all potential leak areas. This is especially true with a gas engine since a vacuum leak will dramatically impact the way it runs. In my experience, as the engine ages, it develops multiple vacuum leaks of varying extent that cumulatively have a huge impact on the engine’s performance. 

Some vacuum leak areas have more impact than others. For example, if the vacuum leak is at the plenum area of the intake manifold, then all cylinders will suffer from a lean mixture to a like magnitude. If the intake gasket is leaking vacuum on only one runner to the cylinder head, then only that cylinder will be impacted but to a much greater extent than a common plenum leak.

Individual cylinder vacuum leaks at the intake manifold gasket or from the O-ring on a port electronic fuel-injection system are very common and often elusive to find without smoke testing. You may be able to find the major leak, but the engine is still suffering from the other lesser offenders.

Light-duty gas vehicles also have an elaborate evaporative emission control system that only handles vapors from the fuel system. These have been in use for more than 20 years. If their integrity is violated due to the age of the rubber lines or damage from driving in the field, the vehicle will have a check engine/service engine light illuminated on the dashboard soon; it may even incur a drivability issue. The evaporative system is almost impossible to diagnose unless the failure is obvious, such as a broken rubber line or fitting. In most instances, the leak is due to porosity – not a clear break.

When it comes to larger diesel engines, a loss of integrity through the induction system is often more elusive. By smoke testing the induction pathway, you can quickly locate leaks in connections and hoses, the turbocharger, and intercooler, along with engine gaskets such as at the intake manifold. Often a series of small leaks in the turbocharger system present as something much more serious and expensive than porous tube connections. 

Other aspects of machinery can be smoke tested such as fuel and hydraulic lines, coolant systems, or storage tanks. 

As with most equipment, there are myriad smoke test machines on the market. They all use a safe chemical to make smoke and may include the ability to introduce a dye to make detection easier. Automotive-style smoke testers usually put very low pressure into the system being tested and rely on the smoke finding its way out. Larger and more complex and costly units will have the ability to pressurize the system to normal operating conditions. These are best for the farm since you can check intercoolers, sprayer tanks and lines, in-shop air and fluid lines, etc. Units with this capability begin around $1,000 and can go up to $3,500 or more. 

A smoke test machine is a great investment that can be shared with a friend or two, allowing the purchase of a larger unit with minimal cost. 

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