As seen on:

SMH Logo News Logo

Call 1300 303 181

Australia’s Best New Car News, Reviews and Buying Advice

Motor Oils Explained

The cheapest part you will ever put in your car is a quart or litre of motor oil. That motor oil will protect your engine against frictional wear, it will neutralize acid build up (a natural byproduct of internal combustion is sulfuric acid), it will suppress corrosion and it helps cool the power-plant. The additive package in motor oils also contains dispersants, detergents, anti-wear agents, viscosity modifiers, anti-foaming agents and pour-point depressants. The latter will allow the oil to pour at very cold temperatures.

Modern engines, transmissions and differentials require modern lubricants to keep them healthy. Think of motor oils, transmission fluids and gear oils as the lifeblood of your vehicle. As the mechanical technology in motor vehicles has increased, so has the need for oils engineered to perform in these technological marvels. The proper selection of a motor oil will keep an engine working properly for many years of service.

Lubricant specifications and performance parameters are enumerated by: the Society of Automotive Engineers (SAE), who established the viscosity requirements; the American Petroleum Institute (API) and the International Standardisation and Advisory Committee (ISAC), who established the service classifications. There is also the Association des Constructeurs European d’Automobiles, which parallels the standards established by the API and ISAC, but mainly for engines of European manufacture.

Don’t be confused by all the initials and oil classifications. Every time there are improvements made to engines, there are also improvements made in the lubricants that protect them. The current motor oil service classifications will protect all current and previous year model vehicles. There are separate classifications for spark and compression ignition engines; gasoline or diesel fueled, but most oils are classified as a multiple use and are appropriate for either type of engine.

Viscosity is the measurement of the internal resistance to flow of any fluid; the higher the viscosity number, the greater the resistance to flow. For warm weather motoring, motor oils with a 30 or 40 viscosity rating are selected. For cold weather driving the viscosity rating should be 10 or 20. The advent of multiple viscosity oil has precluded the need to change the oil in the event of a drastic temperature change. An oil with a viscosity rating of 10-30 means that it operates at low temperatures as a 10 viscosity and when the engine is warmed up and operating at higher temperatures, the oil performs as a 30 viscosity.

Another measurement of a motor oil is the Total Base Number (TBN). Oils are formulated with an alkaline reserve to neutralize acids. When the TBN has dropped to half the original number, the oil should be changed. This usually coincides with depletion of the other additives and will vary in traveled mileage from between 3,000 and 10,000 miles or more. The type of use the vehicle gets determines when the oil should be changed; much stop-and-go driving means change the oil sooner, long highway miles extend the service interval. It doesn’t hurt the engine to change the oil more frequently than necessary. Remember the opening statement of this article.