ForTwo L3-1.0L (2009)
Engine Oil: Description and Operation
BB00.40-P-0222-00A Use Of Single-grade / Multigrade Engine Oils And High-lubricity Oils
- sheet 222.0
1. Single-grade or multigrade oils
Single-grade engine oils SAE 10W, SAE 30, etc. only cover one SAE viscosity class and must among other things be changed depending on the
climate zone and time of year.
The single-grade oils SAE 30 and SAE 40, which are suitable for high thermal loads on engines, make reliable cold starts more difficult or
impossible at low outside temperatures and lead to undesirably high viscosity-related friction losses in the warm-up phase.
In contrast, the single-grade oils SAE 10W and SAE 20W-20 which are very suitable for cold starts are not suitable for use at high outside
temperatures. These low-viscosity oils cannot ensure the necessary protection against wear.
Multigrade oils are engine oils which differ in comparison with single-grade oils by a slight temperature-dependent viscosity change. Due to their
higher viscosity index (lower viscosity/ temperature dependence) they can be used in a relatively wide temperature range.
A correctly manufactured, shear-stable multigrade oil, e.g. SAE grade 10W-40, meets the requirements of SAE grade 10W at low temperatures for
cold flow behavior and SAE grade 40 at high operating temperatures so that the oil change is independent of the time of year (in temperate
climate).
1.1 Conventional multigrade engine oils
During the manufacture of conventional multigrade oils with a mineral oil basis, suitable base oil viscosity index improvers (macromolecular
polymers with an oil-thickening effect) are added. A higher viscosity index or multigrade character of the oils is achieved with these
polymers.
However, the VI improvers result in a non-Newtonian flow behavior. In other words, the viscosity of these oils is not only dependent on the
temperature and the pressure, but also on the shear rate.
Depending on the shear resistance of the oils under high mechanical sheer loads in the engine, the polymer chains may break resulting in a
permanent loss of viscosity in the oils (permanent viscosity drop).
In addition to the permanent sheer loss, a temporary viscosity reduction may also occur, depending on the extent of the shear rate in the
lubricating gap (reversible change in viscosity).
For all multigrade oils, therefore, we require a sufficient shear resistance, so that even after relatively long operating periods an adequate
minimum viscosity is ensured.
It is therefore absolutely necessary to adhere precisely to the restrictions of the operational field of the SAE grades, as specified in the
operating instructions and owner's manuals or on Sheet 224.1/.2.
1.2 Multigrade oils as low-friction oils
In the general public and in the media, so-called "low-friction oils" are gaining more and more significance due to the increasing fuel prices
and the growing oil change intervals.
In the Mercedes-Benz Specifications for Operating Fluids, low-friction oils have been approved for some time. However, these are not
labeled as such on the individual sheets. This is due to the fact that the term "low-friction oil" has neither been standardized nor protected.
Low-friction oils can be formed by lowering the viscosity, by using additives that lower the friction coefficient (friction modifiers) and by the
use of special base oils (synthetic oils or hydrocracking oils).
The European oil specifications currently do not contain any defined engine or laboratory test nor any limits (e.g. for fuel economy) or test
conditions that bindingly regulate the use of the designation "low-friction oil". The term "low-friction oil" on the oil container is entirely the
responsibility and at the discretion of the individual mineral oil companies. It should be pointed out here that there are also different
definitions of a low- friction oil within the mineral oil industry.
Only the multigrade oils in SAE grades 0W-20, 0W-30, 0W-40, 5W-30, 5W-40, 10W-30 and 10W-40 that have measurable fuel economy
potential (with verification, e.g. the M 111 Fuel Economy Test, according to CEC L-54-T-96, compared with the 15W-40 reference oil RL
191). However, these oils must not increase wear, make the engine dirtier, significantly reduce viscosity due to shearing or increase oil
consumption.
For sheets 229.3, 229.31, 229.5 and 229.51, only such low-friction oils are approved which achieve a fuel consumption advantage of at least
1.0 % or 1.7 % in the M 111 Fuel Economy Test (CEC L-54-T-96) compared with the 15W-40 reference oil RL 191.
By using particularly suitable base oils (e.g. synthetic oils or hydrocracking oils) it is possible to manufacture shear-resistant low-friction oils