Using a smoke machine to find vacuum and other leaks.

Using a smoke machine to find vacuum and other leaks.

January 17, 2020 0 By Ray Bohacz

Fluid leaks are usually easy to find, just look for the drips; but vacuum leaks in an engine 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). But 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 why the engine in your combine is not building maximum turbocharger boost or your vacuum meter planter is not working consistently? How would you check the integrity of a sprayer tank and all the lines without filling it with water and running it?

The answer to all these dilemmas is quite simple; use a smoke machine! This apparatus allows for the ability to introduce a nonflammable smoke into a component, quickly revealing the leak(s). Just follow the smoke!

Death by many leaks

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.

From my experience, as an engine ages it develops multiple vacuum leaks of varying extent that cumulatively have a huge impact on its 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 affected 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 illusive 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 gasoline powered 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 twenty years and if their integrity is violated due to age of the rubber lines or damaged from driving in the field, the vehicle will have a check engine/service engine soon light illuminated on the dashboard and may even incur a driveability 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 and not a clear break.

When it comes to larger diesel engines found in farm machines and trucks, a loss of integrity through the induction system is often more elusive than with a gasoline engine.

By smoke testing the induction pathway, you can quickly and easily 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. This is a good protocol when making a repair to confirm its integrity prior to putting everything back together.

As with most equipment there are a myriad of smoke test machines on the market with just as varied a price structure. 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.

Introducing smoke way below system pressure will only locate blatant leaks and not the ones that are elusive.

Units with this capability begin around $1,000 and can go up to $3,500 or more. You will need to shop around and see what unit fits the needs of your farm while also being in your budget.

I view a smoke test machine as an excellent investment but can easily be purchased with a friend or two. Much like an air conditioner charging station, it is not a piece of equipment that you use daily so a co-op investment makes sense, allowing the purchase of a larger unit with a minimal investment.