Engine Oil Viscosity

Choose the right viscosity for your car.

0W Engine Oils

5W Engine Oils

10W Engine Oils

15W Engine Oils

20W Engine Oils

How is Viscosity Measured?

The viscosity of oil changes with temperature, therefore multigrade oils were developed to provide protection across a range of operating temperatures.
The SAE (Society of Automotive Engineers) scale shows the viscosity of oil at both hot and cold temperatures. That’s why the viscosity grade on the oil bottle is made up of two numbers.

Low temperatures

The first number followed by the letter W describes the viscosity of oil at low temperatures (the W stands for winter). The lower the number the thinner the oil.
A thinner oil at low temperatures is good because it flows more easily and is therefore able to protect the engine when it is first started from cold. If oil is too thick when cold, it will not circulate freely and will reduce fuel economy.

High temperatures

The second number describes how thick the oil is at the engine’s normal operating temperature.
The higher the second number, the thicker the oil. If it's too thin when hot, it may not protect effectively. If it's too thick, you lose efficiency.

The correct viscosity grade will be displayed in your car handbook.

Oil specifications

Using the correct oil keeps an engine running smoothly; using the wrong oil could damage the engine, burn more fuel, increase emissions and even invalidate a car’s warranty.
Oil specifications define what type of engine a particular oil is suitable for and its performance against a range of criteria, for example: cleanliness, heat resistance, wear protection, strength. Specifications are regularly updated to keep pace with advances in engine technology. Here’s a look at the four key specification systems:

API (American Petroleum Institute) specifications

The API specifications are a two-letter rating beginning with:
  • 'S' for Service (petrol)
  • 'C' for Commercial (diesel)
The second letter designates the oil’s quality standard, beginning with the letter ‘A’. The further along the alphabet, the higher the oil’s quality. So SL performs better than SA.
Some oils meet standards for both petrol and diesel engines and will be marked with a dual specification, for example SL/CF.

ILSAC (International Lubricants Standardization and Approval Committee) governs international oil specifications, but mainly from a US perspective

ILSAC is made up of US and Japanese automotive manufacturers’ associations, and representatives from key US and European OEMs.
ILSAC specifications often share API requirements, but are additionally focused on improving vehicle fuel economy performance and emission system durability.
The latest specification is ILSAC GF-5. The higher the number, the more recent, and higher performance the specification.

ACEA (the Association des Constructeurs Européens d'Automobiles) governs oil specifications for European cars

ACEA sets the standards for European engine lubricant specification. All oils have to pass a sequence of tests, which are updated on a regular basis as legislation and other demands change.
ACEA specifications cover both passenger and commercial engines and are split into four major categories:
A = Petrol engines
B = Diesel engines
C = Engines needing oils that are catalyst compatible
E = Heavy duty diesel engines

OEM (Original Equipment Manufacturer) specifications are developed by the car manufacturers

As well as the industry standard specifications, most OEMs have their own specific set of requirements for their cars' engines and these are defined in OEM specifications.
To prove that a product meets an OEM specification, oil must pass additional OEM tests. Most OEMs publish lists of all the oils they have approved, so the consumer knows which products are suitable for their vehicle.
These approvals are especially important for cars under warranty.