0w30 vs 0w40 engine oil. What are the differences?

Changing oil is a must when you have to maintain your car’s internal combustion engine, and this has to be done at a certain time or mile number. But because they’re a lot of engine oil types, drivers are always wondering what are the differences between them and which oil is good to use for their engine?

The SAE standards

By viscosity, motor oil is classified by the Society of Automotive Engineers, or, short, SAE. The quality standards and norms of this European organization have long been recognized as international. All motor oil producers are trying to comply with these standards.

You can find the SAE mark on every engine oil tank bought. It stands for the following:

  • the number in front of the letter “w”, an abbreviation for “winter”, that indicates at what minimum temperature the oil retains its fluidity for the winter;
  • the number after the letter “w” displays the maximum possible temperature at which the oil can be applied without worrying that it will no longer cope with the loads due to excessive fluidity.

SAE standards cover many oil characteristics. But only the main ones are listed below:

  • Kinematic viscosity. The ratio of the dynamic viscosity to the density of the lubricating component;
  • Starting properties. Determine what resistance is created by the liquid when the cooled engine is activated, and also whether it is possible to reach the speed required for start at a certain ambient temperature;
  • The degree of pumping. The speed of oil delivery to the rubbing parts of the engine during a cold start;
  • Viscosity at high temperatures. Measured during excessive loads on the car’s motor.

It will be difficult for an inexperienced driver to decode the SAE marking. You might think that if there is a 0 in front of the “w”, then the lubricant will only work at that temperature. In fact, things are a little different.

You can read here more details about engine oil properties

In our case, regarding the oil viscosity at low temperatures: 0w engine oils are used in a temperature range of up to -35 °C or -31 °F, so, you can safely fill it up for the winter.

As for the viscosity at high temperatures:

  • 0w30 oil can do great at high temperatures up to 35 °С or 86°F
  • 0w40 oil can do its job well at high temperatures up to 40 °С or 104°F

Differences between 0w30 and 0w40 engine oils

As a rule, both are universal all-season oils that need to be changed at a certain amount of time (1 year in general) or at a certain amount of miles 9000 – 15000 km or 5600 – 9300 miles.

As it is already clear from the labeling, both oils are 0w products and are suitable for use at extremely low temperatures like -35 °Cup to -40 °C (-31 °F up to -40 °F) or even lower, depending on the composition of the oil.

Their upper range is different, therefore, the fluidity at the engine operating temperature will differ significantly.

The viscosity of 0w30 oil at an engine operating temperature of 100 °C or 212 °F is 9.3-12.5 mm²/s, for 0W40 the indicator should be in the range of 12.5 – 16.2 mm²/s. This indicator tells us that, other things being equal, 0W40 oil will be thicker and will form a denser film on the engine walls than 0w30.

For winter, the use of both 0w-30 and 0w-40 oils are equally good for this purpose and will do their job, the temperature range being somehow small but it can have a great impact on the engine overall, especially in higher temperatures.

Some experiments were made to show what differences are between 0w30 and 0w40 motor oils. So, when comparing those two types of oil from the same manufacturer, in order to avoid inconsistencies in the results, the difference turned out to be obvious.

The most viscous motor oil (the most difficult to rotate the crankshaft in it) turned out to be the 0w40. Slightly less versatile 0w30 turned out to be less viscous at -30 °С or -22 °F by about 9%.

To most motorists, the two viscosities may look the same, but opinions are divided. The most common ones are that 0w30 is a lighter oil than 0w40 and it flows better at low temperatures. Hence, it’s best for cars that don’t see heavy snow or colder weather.

0w40 oil will work in all weather conditions and vehicles with higher horsepower engines since they use more power when the engine temperature is cold because there’s more friction inside the engine which needs more lubrication for the protection of engine parts.

Regarding high temperatures, the differences between 0w30 versus 0w40 motor oil are not so obvious. 0w40 has better resistance to high temperatures and this oil performs terrific in areas where temperatures exceed 100 °F or 37 °C.

Testers appreciated 0w40 oil for its smoothness and how it remained free from gunk on the inside of their vehicles’ engines when they drove in hot weather over several days


0w30 and 0w40 motor oils are suitable to use in winter because they have higher viscosities to operate more effectively at low temperatures.

0w40 motor oil has a slight advantage in very cold conditions. It also performs well in the summertime because of the high performance of this oil in hot climates, and there is less friction as temperature increases during the normal operating range of your car’s engine.

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