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Understanding engine oil grade and viscosity

The viscosity of engine oil is often misunderstood, yet it is one of the most vital aspects to take into account. Choosing the right grade and viscosity of engine oil for your vehicle will ensure you get the best performance and longevity from the engine.

Multigrade oils are given two ratings, the first is followed by a ‘W’ and the second is usually 10,20,30,40, 50 or 60. The ‘W’ in the rating refers to Winter and indicates how the oil will perform under cold temperatures. All oils are thicker at low temperatures, but the lower the ‘W’ number is, the faster the oil will flow in cold conditions.

The second number is the SAE (Society of Automotive Engineers) number, which is measured in centistokes (CST) at 100°C. This number measures the oil’s resistance to flow and is calculated by measuring the time it takes for a standard quantity of fluid to pass through a standard orifice. The higher the value of the SAE number is, the thicker the oil will be.

When choosing the right engine oil viscosity you should always refer back to your manufacturers handbook. Using the wrong oil can lead to reduced lubrication which puts extra pressure on the engine’s components and will shorten its life. Likewise, if the manual says to use synthetic oil, then it is important to follow the recommendations. Engines are designed to run on the right oil specifications and not following these guides can result in problems and even failure of your engine.

Speak to our oil experts who can help you choose the right oil for your vehicle. Call us on 01543 506117 or use our online chat facility.