Viscosity of 10W40 - oil for use all year round
The viscosity of an engine oil whose flow behavior is meant. Viscosity is therefore as thick or as thin liquid is oil. It deals specifically with the viscosities in the SAE standard. It is an engine oil for example for SAE 5W-class, it is a very thin oil (cold temperatures). "SAE 40" on the other hand means that the oil is suitable because of its viscosity even with heat. The 10W40 oil in turn is part of the SAE class "10W40" and is consequently both the cold as suited the warm season.
For each external temperature, the matching engine oil
Which engine oil should be used in a vehicle, is particularly dependent on the respective outside temperatures. If a vehicle is driven in a country like Norway, where in winter can happen up to -25 degree temperatures, a very low-viscosity engine oil of classes SAE 0W or SAE 5W required. If one, however, would fill a thick oil in this vehicle, after a certain period would be more liquid oil in the oil pan, but a solid, candles wax-like substance. The result: Assuming that the motor starts under these conditions at all, the wear would be enormous, because until the engine has warmed up, rubbing metal on metal. However, the reverse can happen. In hot summer temperatures around +40 degrees, the oil would be so fluid that again would rub metal on metal.
Modern multigrade oils such as 10W40 oil solve this problem
Modern multigrade oils with a viscosity of 10W40 distinguished by the fact that you behave at high outside temperatures as a viscous engine oil and when it is cold like a thin oil. The viscosity of 10W40 oil at temperatures below 0 degrees is described by the first figure. When viscosity class 10W40 this is the number 10W - ie: suitable for outside temperatures down to -20 degrees. The second number specification describes the viscosity of engine oil at temperatures above 0 degrees. When 10W40 oil, this is 40 degrees.
Which engine oil is the right one depends on the quality and the manufacturer approvals essentially on the respective outside temperatures. Thus, the 10W40 oil is suitable for temperatures in the range between -20 and +40 degrees, due to its viscosity. If an unsuitable oil chosen a high wear can result.