Image of reduced viscosity engine oil

When API CK-4 and FA-4 were developed, one of the requirements was that lower viscosity FA-4 oils had to meet the same level of engine protection as CK-4 oils.

While both deliver improved oxidation resistance and aeration control compared to the previous generation API CJ-4 oils, FA-4 oils offer the added benefit of increased fuel economy in engines designed for their use.

An important element in meeting or exceeding the standard requirements of both oils is the additive package. It represents 15 to 25 percent of a gallon of oil, with the balance being high-quality base oil. This is higher than the additive levels in passenger-car motor oils designed for gasoline engines.

The role of additives

Additive packages play a crucial role in helping keep an engine clean and protected from varnish and sludge. They also give protection from wear, heat and acids.

Key additives perform multiple vital functions, including:

Acid Control

1) Antioxidants

Engine oils react with oxygen in the air to form organic acids. Oxidation can cause an increase in oil viscosity, formation of sludge and varnish, corrosion of metallic parts, and foaming. Antioxidants help slow down this oxidation process – the main cause of lubricant degradation in service.

Engine wear and Tear

2) Anti-wear additives

Anti-wear additives prevent direct metal-to-metal contact between the engine parts as they lay down a protective, sacrificial film. Using anti-wear additives results in longer engine-life. Why? They reduce wear in the engine. Image shows what happens when there is wear control (left) vs no wear control (right).

Sludge Control

3) Dispersants

Dispersants keep the foreign particles in oil suspended – so they don’t stick together and form a sludge build-up in the engine.

Piston Deposite Control

4) Detergents

Detergents neutralize the build-up of acids, which in turn helps maximize oil-drain intervals. They’re consumed over the life of the oil.

Pour Point

5) Pour-point depressants

The pour point is the lowest temperature at which an oil may flow. Wax crystals that form in mineral oils at low temperatures reduce an oil’s fluidity. Pour-point depressants inhibit wax crystals from forming, allowing the oil to flow at low temperatures on engine start-up.

Engine Oil

6) Viscosity-index improvers

Engine oil viscosity decreases at high temperature (i.e. the oil ‘thins out’), which causes a decrease in the ability of the oil to lubricate properly. Viscosity index improvers keep the viscosity at acceptable levels, which provide a stable oil film even at increased temperatures.


7) Anti-foaming agents

Agitation and aeration of engine oil may result in formation of air bubbles or foaming in the oil. This is particularly a concern in off-highway engines that operate on varied and uneven terrain. Foaming enhances oil oxidation and decreases its lubrication effect and can cause oil starvation. Anti-foaming agents help stop this happening.

A high-quality additive package can help diesel engine oils enhance fuel economy, prevent deposits, and maintain proper flow and viscosity in hot and cold temperatures.

This is important with the increased use of SAE 10W-30, SAE 5W-40, SAE 5W-30 viscosity grades. And even SAE 0W-40 in extreme cold.

Shell Lubricants also tests all its diesel engine oils in harsh on- and off-road conditions to prove their durability and has accumulated hundreds of millions of miles of testing of API CK-4 and FA-4 oils.

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