What does 10W40 mean?

Published 08-06-2021 Jay

What does 10W40 mean?

Engine oil specification. Another conundrum that every car owner has to face. The choice on the market is enormous, so we explain what the various symbols mean. 

10W40 meaning

10W40 oil is a semi-synthetic oil designed to provide optimum protection for the engine. The first number before the "W" indicates winter viscosity. This is how we know how fluid it will be at low temperatures. The next number in turn indicates summer viscosity - that is, the oil's fluidity at high temperatures. As the number decreases, the fluidity of the oil increases. In the case of 10W40 oil, 10W means that the oil will thicken excessively at temperatures below -25 degrees Celsius.  This grade only applies to semi-synthetic oils. They are intended mainly for older types of cars. The second designation - 40 - refers to the most popular summer viscosity class, which is represented by semi-synthetic oils, as well as mineral and synthetic oils. The higher this number, the higher the temperature at which the oil will be too thin to properly protect the engine. 10W40 oil can be used in both gasoline and diesel engines. Moreover, 10W40 is versatile enough to be used in cars with gas installation. 

Can I mix different viscosity oils?

It is important not to change oil parameters. Such a change may lead to very serious damage to the drive unit. The only thing that we can choose and change is the oil manufacturer and the versions of improvements of a given oil type, e.g. some of them have been enriched with a formula that is supposed to prevent the formation of sludge and ensure continuous engine protection. 

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