What characteristics determine the best low temperature oil?

The best low temperature oil will obviously be
one that can get the lubricant to where it’s needed as quickly as possible, while still retaining lubricity at operating temperatures.

Low ambient temperatures affect the flow characteristics of a lubricant. Dropping below the pour point and the higher viscosity not only restricts oil flow to bearings and other machine elements, but also translates into high startup torque. As a result, machines often cannot start or excessive friction causes a complete failure.

Industries and transportation in northern parts of the United States, Europe and Canada are vulnerable to harsh outdoor conditions during winter months. This makes it vital to select the best low temperature oil that will:

• Avoid high churning and splash losses at low temperatures in gear boxes  
• Provide efficient lubrication to bearings and lubricated joints 
• And in a grease, will enable components such as vehicle wheel bearings to safely operate over wide temperature ranges. 

Fortunately, specially compounded mineral or synthetic oils are available that match cold flow requirements, making the selection of the best low temperature oil considerably easier. However, in difficult cases, heating may still be needed for piping, reservoir and filters. In other cases, grease or self-lubricating materials may reduce or even eliminate troublesome low-temperature problems.

What Oil Limits should be considered when selecting the best low temperature oil for the application?

The low-temperature limit for starting an oil- lubricated machine is often specified by the pour point of the oil. This is the lowest temperature at which oil will flow when chilled under prescribed laboratory conditions (ASTM D97). With most mineral-based industrial oils (designated as turbine, hydraulic, industrial and machine oils), this pour point corresponds to the temperature that freezes the paraffin molecules of the oil into a white crystalline wax that will eventually immobilize the overall oil.

Pour point additives that suppress this gelling effect of the wax are used in many automotive oils as well as in industrial lubes. Although gelling is reduced by these long-chain additive molecules, individual wax particles separating out of oil at low temperatures may still plug filters and impede circulation.

With their low paraffinic content, wax free synthetic and naphthenic mineral oils can be further cooled to a lower pour point. At this point the viscosity becomes so high (usually about 100,000 centistokes, cSt) it will eliminate any visible oil flow in the pour point test.

While pour point establishes one low-temperature operating limit, other demanding requirements for low viscosity, such as suction and drain piping, pumps and filters require very careful selection of the best low temperature oil. This viscosity limit represents the highest viscosity at which oil flows and properly lubricates in a system. At temperatures below this limit, the elevated oil stiffness interferes with adequate lubrication and related hydraulic functions in a machine.

By way of example; a large industrial electric motor, for instance, a heavy turbine oil (ISO viscosity grade VG 68) calls for a low-temperature limit of 21°F for the 2,000 cSt machine's viscosity limit. To operate in outdoor temperatures down to 0°F, either heaters would be necessary to bring the temperature above 21°F for starting or the user should switch to a light turbine oil of VG 32 cSt.

While synthetic polyalphaolefin (PAO) or ester-type oils might be considered to be the best low temperature oil because of their superior low-temperature properties, careful consideration should be given to the possible effects on electrical insulation, paint and rubber seals.

Multigrade lubricants have long been considered the best low temperature oil solution.

Multigrade oils have been developed to improve low-temperature startability and to enhance pumpability. A 5W-30, for example, offers low-temperature automotive engine protection in cold engines by exhibiting low viscosity equivalent to SAE 5 oil; whereas in hot engines its viscosity increases to SAE 30.

A 20W-50 oil works well for aircraft engines, where 20W oil provides faster and easier starting in winter and its 50 viscosity protects the engine against metal-to-metal contact when the aircraft is operating under normal conditions.

Similarly, gear manufacturers recommend 75W-90 gear oil for adequate splash lubrication of gear teeth.

These multigrade automotive oils are normally avoided in industrial applications where 15 to 20 percent of the additives are tailored to the demanding conditions in internal combustion engines, which may introduce foam, emulsions and shortened service life.

Nevertheless, some of the best low temperature oil engineered for hydraulic and circulating industrial systems are specially compounded with similar additives to lower the pour point and provide improved viscosity/temperature characteristics.

 Feel free to make use of our professional experience at Habot Synthetic Lubricants when determining the best low temperature oil for your application.