15w40 vs 20w40 motor oil. Differences

Engines are integral parts of a car. A car without an engine is not a car. Therefore it needs utmost care for it to continue serving its purpose.

That is why it is best to know which oils to use on your car engine and those not to use, as not all oils can be suitable for your car. There are different specifications you need to know to choose the best oil for you.

These include the oil’s viscosity index, kinematic viscosity, temperature range, among others. Among the oils that you might consider include 15w40 and 20w40. These two oils and motor oils, but do you want to know which is better for use in your engine? Checkout

15w40 engine oil

15W-40 is the SAE classification for engine oil. This SAE gives various oil descriptions like the viscosity grade and operating temperatures.

The engine oils of the SAE class of 15W40 are multigrade oils featuring excellent flow properties at warm and cold temperatures. Implying that the vital oil lubrication points are supplied optimally at high and low temperatures.

15 W is the oil’s flowability at freezing temperatures. This means the oil can still be pumped even at -25 degrees celsius or -13°F. The number “40” denotes the oil’s flowability at 100 degrees operating temperatures.

This oil’s viscosity range at one hundred degrees celsius ranges between 12.5 to 16.2 square millimeters per second.

Viscosity index

The oil’s viscosity index is 135.

Temperature range

The oil operates at a temperature range of -25 degrees celsius to 40 degrees celsius or -13°F to 104°F. This means that it is best for both cold and warmer operating temperatures.


The oil’s API is Ci-4 Grade.

20w40 engine oil properties

20w40 is the SAE property of this oil, implying that it meets the temperature requirements for twenty weight at and forty weight in hot conditions. 20W is the viscosity or weight of this oil at colder temperatures, while the number 40 is the viscosity or weight of this oil at higher temperatures.

Viscosity index

The viscosity index is ninety-eight minimum.

Temperature range

The temperature range for this oil is -22 degrees Fahrenheit to 122 degrees Fahrenheit or -30°C to 50°C.


SAE 20W40 engine oil has an API of Ch-4.

ACEA properties

A3-98, B3-98, E2-96.

Differences between 15w40 vs. 20w40

  • 20w 40 oil is thicker than the 15w40 oil; therefore best for use in older cars.
  • Since 15w40 is thinner, it is easier to start in colder conditions.
  • 15w 40 has a higher flowability.


  • They both offer good quality lubrication for engines in hotter conditions
  • They both protect against corrosion and wear.

Advantages of 15w40 oil

The 15w40 heavy-duty diesel engine oil performs excellent work in diesel engines. For both old and new engines, this oil creates an outstanding engine performance by enhancing protection against corrosion and wear.

The application of 15w40 engine oil does well to reduce sludge and formation of varnish since it is super anti-oxidation and has high stability to endure high temperatures.

For higher sulfur fuels of more than 500ppm and older engines, 15w40 engine oil is suitable to exceed the warranty period of gasoline and diesel engines.

This oil successfully enhances several engines’ driving and operation performance, such as heavy trucks, farm tractors, light trucks, passenger vehicles, and off-highway diesel equipment.

Disadvantages using 15w40 oil

15w40 engine oil is made best of engines operating in hot environments. However, the engine’s horsepower goes down using such a 15w40 in a cold environment.

What benefits and disadvantages do 20w40 have?

20w40, the multi-grade oil is beneficial for engines in varying temperatures. This oil involves two different oil grades, mono, and multi-grade oil.

In the case where the engine is at a specific flow, that is, cold or warm, monograde oil is applicable. For a case where the engine has two flows, both when the engine is warm and cold, multi-grade oil is suitable. Using 20w40 enhance

  • High terminal stability
  • Extended interval draining
  • Excellent clutch friction performance
  • Anti-wear properties
  • Increased cleaning capacity

Disadvantages of 20w40 to both new and old engines

20w40 engine oil is not suitable to use for engines in colder environments.

Can you mix 15w40 and 20w40?

No, it is not good to mix 15w40 and 20w40 engine oil. These two oils differ in some properties; for example, 20w40 is good at 20°c to 40°c temperatures while 15w40 is suitable below 20°c. When these oils are mixed, their viscosity differences will cause a lack of uniformity in the engine.


Although both engine oils are essential, 20w40 is suitable for old engines. This is because it’s of high viscosity; therefore, it protects the old engines from continuing wearing out. In addition, due to high viscosity, 20w40 is suitable to use in engines in hotter environments.

For new engines, it is suitable to use 15w40 due to its low viscosity and applicability in engines in colder regions.

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