Viscosity, density and pumpability of engine oil

30 August 2021

In the case of engine oil, we can distinguish many of its parameters, for example viscosity and pumpability. Colloquially, we also talk about the "density" of oil, but it is not technically correct. What is the relationship between these concepts and how much do they actually reflect what happens to oil at certain temperatures?

Viscosity is a measure of how easily an oil can flow at a certain temperature. The higher the viscosity, the greater the internal resistance, i.e. the liquid flows slower. Density is a definition of specific gravity and has little to do with the viscosity of the oil. An example would be the comparison of oil to water. Water has a higher density than engine oil and has a much lower viscosity than engine oil at room temperature. The viscosity of oils available on the market is determined according to the standards of the Association of Automotive Engineers (SAE). The classification of oils is divided into winter (described with numbers and the letter "W") and summer (described with only numbers).

“Nowadays, multigrade oils are used in cars - hence, on the packaging you can find two numbers separated by the letter "W". The first one means winter class and fluidity of the oil at low temperatures - for example, Quartz 0W-20 oil spreads much faster on the engine at low temperatures, which means less wear of engine components at start-up and helps to reduce fuel consumption. The second number (after "W") means summer class - the higher the number after "W", the more viscous the oil is at high temperatures. This means that the oil film is thicker, has greater strength, but as the viscosity increases, the internal resistance in the engine increases, which may result in a decrease in power and an increase in fuel consumption. In addition, oils with higher viscosities cool the engine worse, which is very important in the latest, heavy-duty engines” - explains Andrzej Husiatyński, Head of the Technical Department of TotalEnergies Marketing Polska.

Pumpability is equally important to properly distribute the oil over the engine. In the case of oil, we are talking primarily about low-temperature pumpability MRV. It determines the resistance with which oil can flow through the oil channels in the engine at low temperatures. Laboratory tests simulate such conditions that make it possible to confront the properties of the oil with the requirements set by the engine designer. It is also worth mentioning the parameter of high temperature HTHS, measured at 150 ° C. Lower high temperature viscosity means lower fuel consumption. Higher viscosity provides better protection against semi-dry friction and therefore wear, but at the cost of higher fuel consumption and reduced power.

“To prevent the negative effects of lowering HTHS viscosity in places where there are very high pressures, such as between the timing cam and the follower, advanced packages of active anti-wear additives are used in the oil, which react appropriately with the rubbing surfaces to create a very durable lubricating film. Thanks to these additives, we can significantly reduce the viscosity of HTHS without adversely affecting the service life of the engine, thus reducing internal resistance, increasing power and fuel economy, and additionally improving the cooling of pistons and rings, which is very important in the case of high-power engines achieved from small volumes" - explains Andrzej Husiatyński.

It is worth mentioning that the differences in the behavior of the oil do not really become visible until some time later, as the temperature rises. Immediately after pouring it into the engine, they are not visible, so initially you get the impression that oil of one viscosity or another works just as well for a given engine. This is not true. The higher the temperature, the faster the engine oil loses its properties (accelerated oxidation). Oil oxidation deteriorates the lubricating performance and the pumpability of the oil. This process leads to oil thickening and acidification of the oil, increasing its acid number and generation of sludge that can be deposited on engine components or in oil channels. The latter phenomenon, in turn, is favored by the nitration of oil. This is an undesirable condition that indicates that the oil is saturated with nitrogen oxide compounds. Their reaction with hydrocarbons, which are in the composition of engine oil, causes the formation of organic nitrates. This has a destructive effect on the performance of additives in the oil, which are gradually eliminated. For this reason, it is very important to use oils with quality and viscosity parameters exactly as provided by the car manufacturer.

About TotalEnergies

TotalEnergies is a broad energy company that produces and markets energies on a global scale: oil and biofuels, natural gas and green gases, renewables and electricity. Our 105,000 employees are committed to energy that is ever more affordable, clean, reliable and accessible to as many people as possible. Active in more than 130 countries, TotalEnergies puts sustainable development in all its dimensions at the heart of its projects and operations to contribute to the well-being of people.

O TotalEnergies Marketing Polska

TotalEnergies Marketing Polska działa w Polsce od 1992 roku i ma ugruntowaną pozycję na rynku olejów silnikowych. Oferuje produkty dwóch znanych marek TotalEnergies i Elf. Od 2008 roku szybko rozwija również sprzedaż asfaltów, a także jest obecna na rynku przemysłowych płynów specjalnych. Od 2010 roku TotalEnergies Marketing Polska prowadzi import oraz hurtową sprzedaż paliw. W grudniu 2014 roku uruchomiła pierwsze stacje paliw w Polsce, wchodząc tym samym na rynek detaliczny. www.totalenergies.pl

Contact details for media:
Bartosz Cyran | bartosz.cyran@proautomotive.pl | +48 662 454 679

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