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Know your oil

Why is viscosity important? What happens when you use the wrong oil? How do you choose the right one?

The word from members is you want to hear more about products and services that can benefit the workshops. We totally agree so this month we spoke to Shell and are placing the spotlight on oil. 

Oil plays a key role in keeping the engine clean and well lubricated – but not all oil is created equal. Use the wrong oil, and both the efficiency and longevity of the engine may be reduced. The wrong oil may even contaminate expensive emission control equipment. 

Remember that quality counts. It doesn’t matter what sort of fancy marketing goes into engine oil, or how bright and colourful the packaging is, it’s what’s written on the packaging that counts. Specifications and approvals are everything. 

There are two established testing bodies. The API (American Petroleum Institute) being the dominant testing body, and the ACEA (Association des Constructeurs Europeens d’Automobiles) which is the European equivalent. 

You’ve probably never heard of either of them, but their stamp of approval will be seen on the side of every reputable can of engine oil. South Africa uses the API specification to depict the quality standard of the oil and the testing standard.

MIWA spoke to Hein Venter, Senior Lubricants Technical Advisor at Shell, to explain the importance of making the right decision as not all lubricants are created equal. 

Check the performance level

Venter says that lubricants in general, and engine oils in particular, should specify their performance level. Lubricant performance is tested against the industry standard, as well as Original Equipment Manufacturer (OEM) specifications. “Generally higher performance lubricants cost more,” he explains. 

All OEMs specify a minimum performance level for the lubricants to be used in any given vehicle model (either their own specification or a generic industry specification).  It is important to make sure that the lubricants comply to that minimum performance specification.  

“Using the wrong oil in an application can have costly implications, both in terms of inadequate lubrication in the engine itself, as well as contamination of expensive emission control equipment,” he says.  

As a general rule, any oil recommendation starts with the OEM specifications which are normally found in the operator’s manual of the vehicle and as a vehicle owner, that is your starting point. 

The most used industry specification is the API performance specifications. There are two main branches of this specification, the diesel and petrol specifications. The specification for diesel engines are designated with a ‘C’ classification, for example, API CI or API CK.  “The letter after the C indicates the performance level, letters later in the alphabet indicate a higher performance. API CK oils, therefore, perform better than API CI oils, and both better than API CF oils. The latest published specification is API CK,” says Venter.

The petrol equivalent is specified with an S classification. The newest petrol specification (published recently) is API SP.

Viscosity matters

Another very important aspect of engine oils is the viscosity of the oil. This is a measure of the ‘thickness’ of the oil, or how easily it flows. Higher figures represent ‘thicker’ oils, or oils with higher resistance to flow. Viscosity changes (decreases) as the oil gets hot. When the viscosity of a lubricant gets too low (the oil gets too thin) it will fail to protect against metal-to-metal contact, resulting in accelerated wear and possibly catastrophic failure. The OEM of an engine will again specify the minimum viscosity grade to use in that engine.

Modern passenger car engine oils are normally ‘multi-grade’, which indicates it has additives to improve the temperature characteristics over mono-grade oils.  

The viscosity grade of a multi-grade oil is expressed as two figures such as 5W-30, 15W-40 etc. The first figure (before the ‘W’ – for Winter grade) indicates extreme cold viscosity, and the second figure specifies the viscosity at the operating temperature of the engine. It is important not to use an engine oil with a lower viscosity than the grade specified by the OEM.  

Engine oils are generally aimed at either diesel or petrol engines, although there are engine oils with very high petrol and diesel specifications. An example of one of these engine oils is Shell Rimula Ultra Plus 15W-30, which is approved for API SN and API CK.

Oils have various properties which keep your engine clean and well lubricated throughout its entire lifespan and under all possible conditions. The choice that you make when purchasing motor oil will determine the effective use and duration of your engine.

What to ask for at your service station 

So when you next drive up to your service station or workshop and your car needs oil, take a moment to check what is the most appropriate oil for your vehicle and always check the label and look out for the words: Meets the requirements of API SH/CD. Alternatively, look for the API Service Symbol somewhere on the packaging.

A quick guide to the different grades of oil