VS22/Mahn BaugruppelGroup: 00 weltweit DatumlDate:
00 12 07 (381) all countries 06/2007
Arguments concerning engine oil consumption
Customers are often uncertain when it comes to engine oil consumption. Is an engine allowed to consume oil? What are the most important causes of engine oil consumption?
The following explanatory notes are intended as an argumentation aid. They have been compiled for all members of staff in the dealership who have direct contact to customers.
What does the engine oil do?
The engine oil is one of the most important operating fluids in a combustion engine. Without engine oil, the engine cannot operate correctly. The principal functions of the engine oil are:
- Prevention of corrosion and sediment
The lubricating film I engine oil is subject to varying requirements. The engine oil must not have excessively high viscosity at low temperatures to guarantee optimum lubrication even when the engine is cold (e.g. cold start). On the other hand the engine oil must not be too thin at high temperatures as this could cause have a negative effect on the lubricating film, even cancelling the lubricating effect altogether.
The engine oil's most important job is to minimise friction between metallic surfaces. This is realised by a lubricating film that forms between the surfaces of moving engine parts while the engine is running. The thin film of oil greatly reduces friction, leading to reduced wear and less heat generation. Besides preventing pistons from seizing and bearings from being damaged, the service life of all engine parts involved is increased and fuel consumption is reduced.
Another function of the oil film is to seal the combustion chamber from the crankcase via the piston rings.
The pistons reach their normal operating temperature just a few moments after the engine is started. Depending on the ambient temperature, engine configuration and driving style, it may take a few minutes until the engine block, and so the cylinder walls, to reach optimum operating temperature. To prevent the engine from exceeding the operating temperature, it needs a properly functioning cooling system The engine oil is frequently underestimated or overlooked as an important cooling element alongside air and coolant water Yet the engine oil is responsible for a large degree of cooling inside the engine. To cool the piston crowns directly, nearly all BMW engines are equipped with oil spray jets that moisten the piston crowns with engine oil.
Prevention of corrosion and sediment
Not least, the engine oil has the job of protecting the engine against corrosion and sediment. Aggressive combustion residue is neutralised by the lubrication oil and appropriate additives. Other combustion residue is conveyed in the oil circuit to the oil filter where it is filtered out, or it deposits in the oil sump.
Engine oil consumption
Engine oil consumption is determined above all by the configuration of the individual construction groups and systems. It is system characteristic that every combustion engine consumes lubricating oil. The principal causes of this engine oil consumption are:
- Pistons with piston rings
- Valve stem seals
The surface topography of the cylinder liners and piston rings is the primary variable that directly influences engine oil consumption, as the piston rings do not provide perfect sealing, but rather form a metering mechanism In the configuration, there is a conflict of interests between engine oil consumption and friction reduction The latter has a direct effect on power output and fuel consumption With every stroke of the piston, minimal quantities of engine oil remain on the cylinder walls. These are indispensable for lubricating the piston rings (see lubricating film above). As the piston moves downwards, the engine oil on the cylinder wall is plays a role in combustion close to the walls and is then expelled along with the combustion exhaust gases. The higher the engine speed, the greater the effect, because there are more combustion cycles for each time unit. For this reason, engines with a high-speed concept (BMW M engines) tend to have higher engine oil consumption than other BMW engines. The same applies to the lubricating film on the valve stems.
For BMW spark-ignition and diesel engines, the maximum permissible engine oil consumption is 0.7 1/1 000 km.
Because of their increased power output and torque, M engines have a maximum permissible oil consumption of 1.5 1/1000 km.
The measurable result in engine oil consumption is primarily influenced by the quality of the fuel used and the driving profile. For example, if in the winter you drive a lot for short distances (rn high fuel entrainment as the evaporation temperature is mostly only reached briefly) and then a long distance (fuel can then evaporate readily), this journey will cause a considerable drop in engine oil level This is not engine oil consumption but rather a change in engine oil level caused by the fuel content in the engine oil Customer complaints are often the result of this effect It can happen that the engine oil level drops by more than I litre after driving just a few hundred kilometres. Moreover, the measuring system on some engines (dipsticklQLT) have a tolerance of up to 0.3 litres.
But evaporated particles of oil also escape through the crankcase ventilation (expulsion level technically never 100 %) and plays a role in combustion with the intake air Configuration is especially difficult here On the one hand, the engine oil should be expelled as completely as possible. On the other hand, crankcase pressure requirements must be satisfied. Other expulsion systems only work optimally with a certain gas throughput, the expulsion effect deteriorating with greater or lesser gas volumes.
It is a technical necessity that very combustion engine consumes engine oil. The level of the engine oil consumption is greatly influenced by driving style and by the fuel used.
Measuring oil consumption
The oil consumption rate of an engine can only be determined by the customer by the amount of engine oil he or she has had to top up.
Engine oil is added as soon as the level drops below the max. mark on the dipstick, regardless of certain fundamental rules such as horizontal vehicle position, drain time etc. This can easily cause the level to become too high due to the size of the container which happens to be available (e.g. 1-litre bottle).
Excess engine oil can damage the engine and is consumed more quickly due to the "splash" effect.
For this reason, our advice is to allow the engine oil level to drop as far as the mm. mark before adding the required topping up quantity.
The difference between the two marks corresponds to about 1.0 - 1.5 litres.
The procedure for checking the oil level is given in the Owner's Handbook for the vehicle concerned. The service delegates will only deal with warranty claims if exact measurements by weighing are available (please refer to SI 11 07 96 138 / Enclosure 12).
SI Arguments concerning engine oil consumption BMW, MINI BMW AG - TiS 15.03.2009 07:14
issue status (0712006)