Workshops should be careful! New ACEA specifications also have an impact on the selection of lubricants

The technology of modern automobiles is galloping ahead. However, it is not only the electronic systems which are improved and renewed constantly. Also components which have been somehow in the background so far require a knowledge upgrade of the workshops more and more often.

For instance, ever stricter exhaust regulations also call for the development of new engine technologies and exhaust treatment systems.

Because of these technologies the manufacturers of lubricants must adapt the formulation of their engine oils in ever shorter intervals. The continuous trend of special oils for single vehicle manufacturers and models adds to the increased demands.

Modern vehicles can only meet the required exhaust standards if they are operated with the respective lubricants. One typical example are "Low" and "Mid-SAPS" engine oils specifically developed for diesel engines with diesel particulate filter. They possess a low to medium share of sulphated ash, phosphorus and sulphur. For some engine oils the high-temperature-high-shear-viscosity is decreased in addition (e.g. ACEA C1 and C2).

The engine oil specification formulated by the ACEA (Association of European vehicle manufacturers) takes the higher requirements placed on lubricants into consideration. Issue 2008 defines the requirements on engine oils in sequence ACEA C. Based on the individual demands of single vehicle manufacturers it is subdivided into four classes C1 to C4. Basically, they differ regarding the permitted shares of sulphated ash, phosphorus and sulphur as well as their high-temperature-high-shear viscosity (HTHS).

The problem of ash-forming substances
High-performance engine oils used to be based on sulphur and phosphor compounds to achieve the required performance. They are ash-forming substances and their share is limited drastically today. Therefore, lubricant suppliers had to develop alternative agents for the oils to be able to meet the increased performance requirements at all.

The viscosity is one important characteristic value of a lubricant. It influences the oil’s capacity to protect surfaces against wear by forming a lubricating film. Furthermore, it gives the oil’s flow characteristics at a specific temperature. All oils possess their own individual viscosity-temperature-behaviour. This behaviour depending on the temperature is determined by the selected base oil and special additives such as viscosity index improvers (VI).

New standard HTHS viscosity
For modern multi-grade engine oils with VI-improvers the practical viscosity does not only depend on the temperature but also on pressure and the respective shear rate. This shear rate gives the speed at the moved component (in m/s) divided by lubricating film thickness (in m). In order to make more specific/exact statements on oils in practical application one has been using the high-temperature-high-shear viscosity for some years now. It describes the oil’s behaviour in the lubrication gap at an oil temperature of 150 °C and a high shear rate as typical at high engine speed.

ACEA sequence C defines different limiting values for the HTHS viscosity for multi-grade engine oils with VI improvers to ensure the required lubrication also at high oil temperatures and speed. In addition, engine oils with a decreased HTHS smaller than 3.5 mPa*s make a reduction of fuel consumption possible. However, this only applies to engines designed for these oils. One should be careful with older models – here modern oils might do more harm than good.

Similar standards have been issued for engine oils for commercial vehicles according to ACEA sequence E. Classifications ACEA E6 and the new ACEA E9 also call for a reduction of ash-forming substances in engine oils. At the same time they presuppose fuel qualities meeting Western European standards. 

For these reasons workshops should check the specifications for the single vehicle types when buying engine oils and ask their supplier if necessary – this is also recommended by ADDINOL, the German brand with tradition made in Leuna. After all, the "two-drum strategy" – one drum for gasoline and one drum for diesel – which used to be common in numerous workshops, is really water under the bridge today.

ACEA: Engine oil classes
ACEA (Association des Constructeurs Européens d’Automobiles = Association of European vehicle manufacturers) issues its own oil standards (last update in 2008). These are meant to better comply with the requirement and performance level of European engines than known API classes. In addition, environmental protection is important in the ACEA standards. All in all there are 4 categories: A for gasoline engines, B for diesel engines in passenger cars, vans and transporters of small volumes, C for diesel engines in passenger cars equipped with particulate filter and E for diesel engines in trucks. Categories A and B are classified into the groups A1 to A5 as and B1 to B5. There are also respective categories for transmission oils.

German article published in kfz-betrieb 14/2011 (view German article here)

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