What Are the Substitutes of Vacuum Pump Oil?

Vacuum pump oil is well-refined mineral oil (usually) with low vapor pressure and a particular viscosity that separates them from the rest.

Vacuum pump oil is not just derived from distilled petroleum products. Presently you can see silicone-based synthetic oils, that may have a low sulfur content. Hydro-treated oils are also quite common. 2x or 3x distilled oils are available too.

Keeping in mind the anti-oxidant, anti-foaming, and corrosion-resistance of the oil, there may be a few substitutions to the vacuum pump oil. I will discuss them in detail in this article.

Why Do You Need Vacuum Pump Oil?

The function of this oil is to keep your vacuum pump lubricated, therefore, functional. It also collects moisture and contaminants from the systems.

The vacuum pump lubricates the gear mechanism. This is seen in dry pumps, e.g: screw pumps. In oil-sealed vacuum pumps, we see the oil create a smooth rotation cycle.

Requirements to be a Good Vacuum Pump Oil

Different engine environments require different types of vacuum pump oils. Selection is therefore crucial. You shouldn’t use a hydrocarbon-based fluid in an oxygen-rich environment. Because it allows for oxidation of the fluid and the formation of toxic products. This will be degrading to the pump.

In this case, a non-reactive line of fluids should be used. Some fire-resistant fluids are also available for automotive applications.

Substitutions for Vacuum Pump Oil

Whichever oil you choose, keep in mind that you must maintain the viscosity. Because too thin an oil will not provide proper lubrication. Similarly, too thick an oil can hamper the lubricative functions.

An ISO 22 or ISO 32 viscosity is necessary for liquid ring vacuum pumps. An ISO 68 (SAE 20) or ISO 100 (SAE 30) oil is necessary for rotary vane vacuum pumps. Process pumps require an ISO 220 (SAE 50) viscosity.

Although, vacuum pump oils are very specialized, what can be the substitutes for a vacuum pump oil?

Refrigeration Oil: You can use any refrigeration oil instead. For example, Suniso 3GS. It’s specification is 155 SUS/38*C. it is a light mineral refrigeration oil. It’s Pour point and Flash point are respectively -40 oC and 168 oC.

Hydro-treated/Hydrocracked Oils: They are hydrotreated Vegetable Oil (HVO). It is a biofuel made by the hydrocracking or hydrogenation of vegetable oil. The process breaks big molecules into smaller ones using hydrogen. Meanwhile, hydrogenation adds hydrogen to molecules.

Polyalphaolefin (PAO): These aresynthetic oils. PAOs have exhibited outstanding high and low-temperature performances. They have good oxidative and thermal stability. Their compatibility with mineral oils and maximum synthetics is also commendable.

Motor Oil: You can use straight 30 weight, non-detergent motor oil as a substitute for vacuum pump oil.

Esters: Both diesters and POEs are included in this category. Both are forms of synthetic oils. These are more thermally stable. They are commonly used in applications with the presence of higher temperatures.

These oils prevent varnishing or the build-up of sludge because of their high polarity. More advantageous is their cleaning ability. They act as a natural detergent.

A Comparison Chart for Compatible Substitutions

Fluid Characteristics Temperature Range Affordability
Refrigeration Oil
  • Constant thermal conductivity.
  • High natural viscosity index.
  • Thermal and Chemical stability.    
– 400C to + 150C. Cheap to Moderately Expensive
Hydro-treated/Hydrocracked Oils
  • Good low-temperature properties.
Very low temperatures. Cheap to Moderately Expensive
Polyalphaolefin (PAO)
  • High viscosity index.
  • Good thermal-oxidative stability.
  • Low volatility.
  • Compatible with mineral oils.
-60 to 125°C Cheap
Motor Oil
  • High viscosity index
  • Thermal stability
  • Oxidation stability
100 to107°C Cheap
  • Thermally stable.
  • High temperature tolerant.
  • Prevents varnishing or the build-up of sludge.
  • High polarity.
  • Natural detergent.
180 to 230°C Expensive

Which Substitute to Choose?

Judging from the above comparisons, I would suggest going for Ester oils. They are good substitutes that can also be cheap. In fact, esters are superior to other synthetic oils. Additionally, they provide good solvency.

Although they are a bit expensive ( ingredients collected from all-natural sources ), it delivers a better performance overall. They are green-friendly too as they are 100% renewable!

What Happens If You Run A Vacuum Pump Without Oil?

All vacuum pumps require a good supply of lubricating oils. The insufficient supply of this oil causes damage and malfunctioning of the vacuum pump. The pump will wear out in a short time. The jamming of the vacuum pump can occur. This in turn will cause damage to other parts of the vehicle.

The temperature of the engine may increase and the vehicle might suffer from overheating. A dry pump will definitely damage the internals.

Can You Add Oil To A Running Vacuum Pump?

When adding oil to the vacuum pump, it is suggested that the pump is at a hard vacuum. This ensures smooth addition of oil, avoiding all messes. You must use the correct oil for the correct level too while refilling.

First, plug in the pump. Then start adding the oil. Finally, top off while the pump is running.

So yes, you can, and you should add oil to a running vacuum pump.

How Often to Change the Vacuum Pump Oil?

As you already know, vacuum pumps can trap contaminants. While some can be exhausted out of the system, others tend to remain trapped. This eventually decreases the performance of the vacuum pump.

Therefore, it is necessary to change the vacuum pump oil whenever it has been contaminated. But how frequent is that?

One of the indicators of an oil change is the pump level jumping above and below. Add oil discoloration to the list of ‘pretty obvious symptoms’. Hydrocarbon oils tend to darken or become creamy-ish. Also, the vacuum pump not reaching the desired vacuum level is another sign. 

Please be careful about replacing and discarding the oil in authorized locations only. Try to be as green-efficient as possible.

Final Words

On an ending note, I would like to suggest you to stop looking for vacuum pump substitutes. It is a very specific oil and the balance of viscosity is very important.

But often you will not find a vacuum pump oil nearby. Because vacuum pumps usually derive lubricants from the engine. However, using a proper vacuum pump oil is important, no matter what you hear conventionally.

I hope this article will help you with substitutes for vacuum pump lubricant in times of a dire need!

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