Engine oils

Unalloyed engine oils vs. HD monograde engine oils

Today, there are still unalloyed monograde and multigrade engine oils whose area of application is primarily limited to engines without a main-flow oil filter.

What is behind this?

In the early days of motorization, engine oils that allowed oil sludge to form were required according to the state of the art at the time. This was so important because unwanted and oil-insoluble foreign substances accumulated in the oil sludge, which, if left in the engine oil, increased mechanical wear on bearings and cylinder running surfaces and thus reduced the lubricating effect of the oil. In unalloyed engine oils, however, the oil sludge is deposited at the bottom of the oil pan, preventing these substances from returning to the oil circuit.

What do the additives do?

Compared to unalloyed oils, HD oils are mixed with additives. These additives prevent the formation of oil sludge, which is extremely important in vehicles with oil filtration, as the bound foreign substances are filtered out of the oil.

The additives contained in HD monograde engine oil also have a cleaning effect. In older vehicles, oil carbon deposits were already expected during the design phase. Removal of these deposits by cleaning additives would lead to unwanted blockages in the oil ducts due to a lack of oil filtration and, in the worst case, engine damage.

Monograde engine oil

Until the 1970s, monograde oil dominated the market. Every oil on the market had its own specific fluidity and was labeled with this. Motor vehicle engines were operated with oils of viscosity classes SAE 20, SAE 30, SAE 40 or SAE 50. Monograde oils with their guaranteed minimum viscosity still make sense today, especially for older series engines, which are sometimes designed with large tolerances and running clearances.

Multigrade engine oil

The vast majority of engine oils commonly used today are so-called multigrade oils. These are based on low-viscosity base oils and are mixed with special additives in such a way that their viscosity only decreases slightly at higher temperatures. This results in a high lubricity of the cold oil during cold starts, a lower load on the starter motor at low temperatures and a sufficiently high lubrication reliability at higher outside and engine temperatures. This means that the same oil can be used in both summer and winter operation, which was not possible with the monograde oils used in the past.