The test oil is timed as to how long it takes to travel through a glass tube. (You may see it shown on specification sheets as mm2/s). It is named after an Irishman called Sir George Stokes from the 1840s. Kinematic viscosity is measured in Centistokes cSt. Kinematic viscosity – measures the normal operating temperature viscosity – it is measured at 100☌. They both have their uses.Ĭoncept 2 – Kinematic viscosity is used to measure the second number – 30 in our example The first way is called Kinematic viscosity and the second way is called Dynamic viscosity. The oil chemists measure viscosity in two different ways. I know we don’t usually put honey in the microwave, but it works for this article. “You mean like honey taken out of the freezer compared to honey taken out of the microwave”. A delegate once said to me when I was doing automotive oil training. The other crucial point is that oil thickens up when it gets colder. Or put simply, is the liquid thick or thin? Take water and honey no misunderstanding here. Viscosity is the fluids resistance to flow. We need to have a better an understanding of what viscosity is, before moving on to defining how we measure it. The second number, the 30 is the viscosity at normal operating temperature. Most of us know this is the cold start rating. High Temperature High Shear viscosity HTHSĬoncept 1 – What is viscosity and what does, for example, 0W-30 really mean?.We are going to look at four key concepts relating to automotive oil viscosity. The odd thing about viscosity is if you ask 10 people and there will be 10, possibly 11, different answers. We need to adopt the brace position or as Eddy Murphy said in Beverley Hills Cop 2…We are going deep, really deep! Welcome to the lubricious world of automotive oils. Yes, I do understand oil viscosity…….or do you? Online exclusive feature for .ukīY: Simon Michell, Lubrication expert and freelance industry consultant at Unquenchable