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Ok this question must have been asked loads of times, but what do the numbers on oil mean?

10-40 means it should be run in 10-40'c outside temperature? to remain at a certain viscosity, or am I wrong? and it means something else?

Actually the 10w40 refers to the viscosity (or thickness ) of the oil.The 10 means that the oil will act like a 10 weight oil in cold temperatures and act like a 40weight oil in higher temperatures.Because it is a multi-grade oil it has to blended with polymers and other chemicals to acheive the desired effect.One of the downfalls is that the wider spread of numbers (0w40,10w50 etc) as compared to narrower range oils (10w30 20w40) require more additives which can break down causing a viscosity failure of the oil at high temperatures and load.Oils such as 10w40 are recommended for most engines as it will cover pretty well any temperature range a motorcycle is likely found to be operating in.I could go on for days about oils talking about their functions and additives and which is better but I won't.Just remember to use a motorcycle specific as they are designed for use with wet clutches and transmissions while regular car motor oil is not and could have additive packages that are not compatible with the clutches.

There's plenty people(myself Inc)
Who've used cheaper car oil for 10s
Of thousands of miles to no ill effect.
With the saving you can change every 2000 miles.

What you need to know about oil:  1. Read the manufactures recommendations/specifications2. Follow the recommendations to the letter. as for the viscosity numbers: Oil Viscosity is a measurement of the resistance of a fluid being deformed by either shear stress or extensional stress. It can also be thought of as a measure of fluid friction. There are many different types of ways of expressing a fluid's viscosity. one way of calculating this is to calculate the fluid's kinematic viscosity. The kinematic viscosity is the ratio of the viscous force to the inertial force (or density). It can be defined as:

  • v = Kinematic Viscosity (cSt [Centistokes])
  • µ = Absolute Viscosity (cP [Centipoise])
  • ρ = Density (g cm -3 [grams per centimetre-cubed])

 Simply speaking, the lower the viscosity value, the thinner the oil will be. Which follows that a high viscosity value indicates a thicker oil. For example, water has a viscosity of about 1 cSt. An average engine oil has a viscosity of about 100 cSt.Viscosity is a very important property of oil that allows it to protect the internal workings of a machine by creating a thin film of oil between moving parts. Viscosity can be affected by many factors and so regular monitoring is essential. The test is generally carried out on industrial machinery such as engines, hydraulics, gearboxes etc.Oil is a non-Newtonian fluid, which means that its viscosity is not constant - it cannot be described by a single number - it varies. For example, a temperature increase by only 5°C can cause the viscosity of some fluids to double! OCLS checks viscosities routinely at 40°C, but other temperatures up to 100oC are used. Oil viscosity can be affected by many factors and so regular monitoring is essential.

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