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" Multigrade Machinery Oils "

To better understand what multigrade oil is, we first have to explain some basic terms of the engines:

Oil Viscosity Oil
viscosity is best described as the oil's resistance to motion. The more fluid (thin) an oil, the lower its viscosity. A viscous oil moves much harder and therefore its viscosity is higher. According to ASTM-D-445, the viscosity is measured in Centistokes (CSt) at 40 and 100 degrees Celsius.

SAE Oil Classification
The SAE (Society of Automotive Engineers) has created viscosity ranges from 0 (zero) to 70. The lower tiers (up to 25) bear the forward 'w' for winter - winter, suggesting that engine oils of these stages are suitable for use in winter and at low temperatures.

Viscosity Index (VI)
The Viscosity Index is defined as the change in viscosity of an oil based on temperature. It is measured according to ASTM-D-2270 and is a clean number. The higher the Viscosity Index, the less the oil viscosity is affected by the temperature changes. Mineral oils typically have a viscosity index around 95 whereas synthetic lubricants can have around 150.

Multigrade Engine Oil
It is the engine oil where, with the addition of chemical additives and viscosity improvers, we are able to maintain the viscosity constant over a wide range of temperatures. The most common multi-stage engine oil is the SAE 15w-40. Its name means it is SAE40 oil but at low temperatures it has a viscosity similar to a SAE15w oil.
This is very important because at the start of the engine the oil moves more easily (lower viscosity) and reduces engine wear while at normal operating temperatures we want the lubrication and viscosity of a more viscous lubricant such as SAE40 or SAE50.

Explanation of Graphics
Two SAE10w (blue) and SAE30 (red) engines are shown next to each other as well as their viscosity decreases in relation to the increase in oil temperature (direction to the right). We also see that the SAE30 is much more viscous than it should at low temperatures, while at high temperatures the SAE10w viscosity decreases so much that it would be dangerous for the engine.

Multi-grade SAE10w-30 oil keeps its viscosity stable over a wide range of temperatures. As shown in the dashed green line graph, the viscosity of SAE10w-30 remains within acceptable levels at both low and high temperatures.

Machine oils are becoming thinner
We need to make it clear that the evolution of the engines always follows the evolution and requirements of the engines. The trend for ever-thinner engine oils (eg SAE0w-30) is dictated by the tendency for ever-smaller machine-sized engines that are becoming increasingly narrow in oil circulation.

This necessity has prompted engine manufacturers to develop synthetic engine oils with very high Viscosity Indicators that despite their particularly low viscosity at low temperatures, they can have the lubricating capability required by increasingly stressed machines at normal and even higher operating temperatures .

Synthetic engine oils have been engineered to work at higher temperatures than regular mineral oils. At higher temperatures, normal oils are rapidly oxidized and lose properties quickly.

Note: LUCAS OIL has developed a special OIL STABILIZER for synthetic engine oils.