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Oils and Lubes

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Whether you drive an old or a new vehicle, oils and lubricants for your engine, diff and gearbox are critical factors affecting performance and also your running costs. In this article we have concentrated purely on the key issues, have avoided mention of brands, but have highlighted certain facts relevant to the audience of ExplorOz - more than likely you're a 4WD owner and a traveller.

What Does Engine Oil Do?

How Do Engines Use Oil?

Choosing Engine Oil

Conventional Oil

Synthetic Oil

Synthetic Oil Blends

Additives in Oil

Use of additives is an approach to improve and maintain oil performance. Because high engine temperatures will combine with moisture, combustion by-products, rust, corrosion, engine wear particles and oxygen, sludge and varnish will be produced. The role of oil additives will not only assist in maintaining good lubrication, but also help minimize sludge and varnish, and any damage that would occur to your engine as a result.
There are hundreds of oil additives on the market. Some say that they will reduce your mileage, or reduce your wear, or reduce your oil consumption, and some even say that you can run your engine without any oil after treating your engine with their miracle cure additive.

Keep in mind that the base oil package in any oil can range from 70-95% of the mix, the rest comprised of additives. However, since some base oils will actually have natural characteristics which reduces the need for additional additives, comparing % of additives between different oils doesn't mean anything.

The ingredients in an additive package differ in cost, but price is just one factor. Some work better in certain combinations of base oils, and some of the less-expensive base oils are a good choice for a blend because of the way they perform with popular additives. Bottom line: every motor oil has a recipe. Refiners come up with a list of objectives based on the needs of their customers (vehicle manufacturers) and formulate oil to meet those goals as best they can.

Detergents

The purpose is to keep the surfaces of your engine parts clean by inhibiting the formation of high-temperature deposits, rust and corrosion.

Dispersants

These additives disperse solid particles, keeping them in solution, so they don't come together to form sludge, varnish and acids. Some additives work both as detergents and dispersants.

Antiwear Agents

There are times when the lubricating film breaks down, so the antiwear agents have to protect the metal surfaces. A zinc and phosphorus compound called ZDDP along with other phosphorus (and sulphur) compounds are commonly used.

Friction Modifiers

These reduce engine friction and therefore can improve fuel economy. Graphite, molybdenum and other compounds are used.

Pour-Point Depressants

Oil contains wax particles that can congeal and reduce flow, so these additives are used to prevent that occurring.

Antioxidants

This prevents oxidation (thickening) of oil. Some of the additives that perform other functions also serve this purpose, such as the antiwear agents.

Foam Inhibitors

The crankshaft whipping through the oil in the pan causes foaming. Oil foam is not as effective a lubricant as a full-liquid stream, so the inhibitors are used to cause the foam bubbles to collapse.

Rust/Corrosion Inhibitors

Used to protect metal parts from acids and moisture.

Oil Terminology

Below is a list of terminology that you may come across in regards to engine oil.

Viscosity

Viscosity is a measure of the oil's thickness/resistance to flow. There are 2 numbers in the viscosity rating - eg. 30W-50. The first number relates to viscosity at cold temperatures, and the higher the 2nd number, the more resistant it is to thinning. Within reason, thicker oil generally seals better and maintains a better film of lubrication between moving parts.

Generally, if viscosity is too low, oil can sheer and loose film strength at high temps. If too high, oil may not pump to the proper parts of the engine when temps are low and the film may tear at high rpm. So 10W-30 oil has less viscosity when cold and hot than does 20W-50. What's really important is that you use the oil viscosity your car's owner's manual recommends.

Multiviscousity

Multiviscous oils are one of the great improvements in oils but choose wisely - these oils are more prone to viscosity and thermal breakdown due to the high polymer content. For an engine used fairly little, when oil changes are infrequent, multi-viscosity oils are important so that lubrication is adequate in either winter or summer. The rule of thumb when selecting a multiviscous oil to select one with the narrowest span of viscosity for the temperature you will use it in.

Viscosity Index

Resistance to thinning with increasing temperature is called viscosity index. This is a number that indicates the rate of change of viscosity for a given temperate range. Again, generally the higher the number the better.

This property of oil is a major contributor to the life of your bearings. And although a higher second number is good, the oil also has to be robust. For example, oil tends to lose viscosity from shear, the sliding motion between close-fitted metal surfaces of moving parts such as bearings. So resistance to viscosity loss (shear stability) is necessary to enable the oil to maintain the lubricating film between those parts.

Flash Point

This is the temperature at which an oil gives off vapours that can be ignited. Flash point can be an indicator of the quality of base stock used. The higher the flash point the better (this property affects volume of oil consumed by the engine).

Base Oil

The base oil is that which is used in the formula before additives are introduced to make up the entire oil formula. Both synthetic oils and petroleum oils can be made from paraffin base oils.

Paraffin

Paraffin is recognized as the best lubricating oils and offer a number of advantages over napthenic oils. High quality 100% paraffinic oils are the best type of base oils. Both paraffin and napthenic are types of petroleum oils.

Pour Point

More of a winter issue for climates where freezing is likely. Basically, this is a number indicating a temperature level when the oil is too thick to move. The lower the pour point the better.