Effects of temperature on engine lubricating oil
The effect of temperature on engine lubricating oil is an important consideration to take into account when operating a large fleet of vehicles. Except for electrically powered units, all vehicles are powered by a combustion engine of some description, be it fuelled by gas, petrol or diesel.

All engines require some form of lubrication and this is provided by the oil. This oil is required to carry out numerous different tasks when the engine is in operation, the primary function being to lubricate all the components by reducing friction and preventing or reducing metal to metal contact. The oil stops two components' surfaces from touching one another as illustrated in Figure 1 and Figure 2.

In an endeavor to achieve the best possible friction reduction at normal operating temperature, oils are formulated with specific base stocks and additives in order to carry out specific jobs within the engine. These oils are designed to function in an optimal way at the normal operating temperature range of the engine. As a general rule of thumb, an engine oil's operating temperature should be approximately 10°C to 15°C above the cooling water temperature. Keeping this in mind, the sump operating temperature of the engine oil should not exceed 105°C under normal conditions.