A noticeable effect can be achieved in other ways - for example, using energy-saving oils.
FRICTION OF THE PARTIES
Of course, engine oil is not able to improve mixture formation or reduce the so-called pumping losses (resistance to gases at the inlet and outlet), therefore, all the savings are achieved by reducing friction losses between engine parts. Two boundary lubrication regimes can be distinguished here: hydrodynamic, when the parts are separated by a relatively thick “oil wedge”, and boundary when the thickness of the oil film is insufficient to exclude contact of their surfaces.
The first mode occurs, for example, in the sliding bearings of the crankshaft and camshaft. The second - in pairs "cam-pusher" and "piston-cylinder" near the dead points, when the speed of movement of the piston is low. Each mode has its own “energy-saving” mechanism.
Losses in the hydrodynamic mode are reduced, reducing the viscosity of the oil - mainly at low temperatures, where it is obviously excessive. This is facilitated by a low-viscosity base and special thickening additives. In addition, the viscosity of such oil decreases with an increase in the speed of relative movement of parts, when the oil wedge already holds the load well.
Friction in the boundary mode is reduced by the addition of modifiers: solid (graphite, molybdenum disulfide) or liquid chemical compounds that form an antifriction coating on the metal surface.
PURE SAVING
Energy-saving properties of engine oil are indicated in its labeling. According to the API classification (American Petroleum Institute), such oils are denoted by the letters EC (Energy Conserving) or FE (Fuel Economy) after the category of operational properties: for example, SAE 5W-30 API SL / СG-4 EU. The Roman numerals after the letters indicate the degree of "economy" in comparison with the reference oil 15W40: EU I (or simply EU) - up to 2.7%, EU II - over 2.7%. In the 2002 ACEA classification, energy-saving oils are divided into separate categories: A1–02 and A5–02 for gasoline engines and B1–02 and B5–02 for diesel engines of cars and light trucks. Compared to the reference oil, they should provide a reduction in fuel consumption of at least 2.5%. Actual savings depend on driving conditions and temperature. In the city, it ranges from 3-5%, on the highway - 1.5-2%. In winter, the reduction in consumption is even more noticeable. And the use of such oils in the transmission gives an additional gain of 2–2.5%.