"I always thought" Serge I could not remember the answer to that myself, so I went to the net and looked up oil viscosity and got the following site http://auto.howstuffworks.com/question164.htm The long and short of it is stated in their example The viscosity grade (for example, 5W-30) tells you the oil's thickness, or viscosity. A thin oil has a lower number and flows more easily, while thick oils have a higher number and are more resistant to flow. Water has a very low viscosity -- it is thin and flows easily. Honey has a very high viscosity -- it is thick and gooey.
There is probably a specific temperature that the testing is performed at. The W in 5W-30 says the oil can be used in Winter. " Viscosity is ordinarily expressed in terms of the time required for a standard quantity of the fluid at a certain temperature to flow through a standard orifice. The higher the value, the more viscous the fluid. Since viscosity varies inversely with temperature, its value is meaningless unless accompanied by the temperature at which it is determined. With petroleum oils, viscosity is now commonly reported in centistokes (cSt), measured at either 40°C or 100 °C (ASTM Method D445 - Kinematic Viscosity). " Orma Southfield, MI N110LR Tweety, old enough to drink this year Flying and more flying, to the gathering or bust http://www.kr-2.aviation-mechanics.com/
