Part 1
BB00.40-P-0221-00A Requirements In Respect Of Engine Oils
Constant developments in combustion engines demand that engine oil too keeps pace with the technical status at any given time of the engines both in terms of its properties and performance. Engine oil is an important, decisive and integral design element for the function and service life of an engine and therefore it must comply with the technical quality standard of an engine. Engine oil is expected to fully fulfill its intended tasks, which extend well beyond the sole function of a lubricant, under all kinds of occurring operating conditions - at least until the scheduled oil change deadline.
The basic requirements placed on engine oils are initially specified verbally in the following list and not in the form of tests and limit values. The requirements are divided into 8 topics. It is obvious that several requirements partly overlap or that they cannot be viewed independent of each other. The given sequence of requirements does not represent any form of priority. Depending on the engine model and the operating conditions the various points will have to have a different emphasis placed on them.
Area I - Friction and wear
1. Friction reduction
2. Fuel consumption reduction
3. Wear protection
4. Oil film tensile strength
5. No surface damage (pitting)
6. Preservation of honing pattern
7. Matching additive reaction temperature
8. Neutralization capability
9. Grip
Range II: temperature and viscosity
10. Thermal stability
11. Oxidation stability
12. Nitration resistance
13. High-temperature viscosity (shear rate, pressure)
14. Low-temperature viscosity (overflow, pumpability, continuous flow, no air inclusion)
15. Low temperature-dependent viscosity change
16. Viscosity stability (mechanical, thermal, oxidative)
Range III: purity
17. Dispersing power
18. Detergency
19. No ring riding/no ring sticking
20. Prevention of hot sludge
21. Prevention of cold sludge
22. Prevention of paint
23. Resistance to water
24. Resistance to antifreeze with corrosion inhibitor
Range IV: no residues
25. No deposits on intake valves
26. No residue formation in combustion chamber
27. No glow ignition
28. No deposits in vicinity of turbochargers
Range V: oil/engine components
29. Corrosion protection
30. Compatibility with metals and paints
31. Compatibility with elastomers (seals)
32. Compatibility with filter materials
33. No blocking of filters
34. Thermal conductivity/cooling effect
35. Sealing capability
Range VI: Base oil/additives
36. Solubility of additives
37. Homogeneity
38. No filtering out of additives
39. No heat development
40. Prevention of foaming
41. Air emission capability
42. Low volatility/vaporization tendency
Range VII: application
43. Fuel consideration
44. Miscibility/compatibility
45. Running-in characteristics
46. Long change intervals
47. Applicability in different types of engine (manual transmissions, hydraulic systems)
48. Consistent quality
49. Inexpensive manufacture
50. Availability
51. Storage capability
Area VIII: Environment
52. No negative effects on health and the environment
53. No negative effects on exhaust after treatment systems
54. No contribution to particulates
55. Does not emit odors
56. No disadvantages with regard to disposal and recycling
Explanations on the individual items in the areas
Area I - Friction and wear
1. Friction reduction
As with every lubricating oil, engine oil is obviously intended to prevent friction as far as is possible. A low engine friction horsepower contributes to improving efficiency; the output generated by the engine should primarily be available to propel the vehicle.
2. Fuel consumption reduction
Because the saving of energy has become the main focus of interest, engine oils must thus also play their part in helping to further reduce fuel consumption levels. A fuel consumption saving is possible, in particular during the warm up period, i.e. in the time between the cold start and reaching operating temperature.
Through the choice of suitable additives it is now possible to exert a positive influence on friction-related conditions.
In the development and application of such oils, which are to be welcomed in principle, attention must however be paid to the fact that no disadvantages of any kind whatsoever arise, in particular in relation to the engine's service life. With regard to the individual car driver, the fleet owner and the national economy these oils must of course realize both financial and energy-related advantages. On no account should the fuel-consumption level rise.
3. Protection against wear
In order to ensure that an engine achieves as high a mileage as possible without suffering any performance loss or increase in oil consumption, mechanical and corrosive wear must be prevented as far as is possible. This applies in particular to cylinder contact surfaces, pistons, piston rings and the valve timing (cams, tappets, cam followers or rocker arms, chains etc.). In many cases friction bearings are the limiting factor in the service life of an engine element, and for this reason they have to be especially protected against wear.
4. Oil film tensile strength
Even under the greatest of loads and at the highest of temperatures the oil film, e.g. between the piston ring and cylinder contact surface, must not break down, because direct metallic contact can lead to "seizure" and thus to a total loss.
5. No surface damage (pitting)
The engine oils must protect all components from any surface damage and should not cause any such damage themselves. This applies in particular to pitting on tappets, which can lead to damaging the cams.
6. Preservation of honing pattern
A well preserved honing pattern on the cylinder contact surface is essential for ensuring a controlled oil consumption. For this reason "bore polishing" or "deposits" must not occur. This is absolutely essential for a long service life.
7. Matching additive reaction temperature
The oil additives used for protection against wear do not achieve this solely on account of their presence, but rather through a chemical reaction on the surface of the components.
Therefore, one has to make sure that the reaction temperatures of the additives match those operating temperatures (and pressures), e. g. that are prevalent on the cams.
8. Neutralization capacity
Gasoline fuels and, in particular, diesel fuels contain sulfur. During combustion of this sulfur content the fuel may give off sulfurous acids or sulfuric acid together with combustion water. This must on no account take place, and therefore such acids must always be immediately neutralized.
Engine oil must also be alkaline; this alkalinity is partially reduced during the neutralization process, however a certain residual alkalinity must be retained until the next oil change is due.
9. Adhesive force
If the engine is switched off during full-load operation at a high temperature, a residual oil film must remain at the lubricating points, so that a subsequent start-off in a cold condition does not lead to damage as a result of "running dry".
Area II - Temperature and viscosity
10. Thermal stability
Engine oil must exhibit thermal stability at whatever temperature; it must not alter in an unfavorable way.
11. Oxidation stability
Because oxygen is always present as a result of the high temperatures in the engine compartment, the oil must be oxidation resistant; it must not lose its advantageous properties and not form any natural oil oxidation products or residue. This would lead to a rise in the oil's acidity level and to the oil thickening. Thickening oil causes problems when cold-starting and increases the fuel-consumption level.
12. Nitration resistance
During combustion, nitrogen oxide is formed, which acts upon the oil together with the blow-by gases. This in turn can lead to a nitration with subsequent sludge formation. Ever since the arrival of the "oil-sludge problems" one is aware of how important nitration resistance is.
13. High-temperature viscosity
To preserve the minimum lubricating film that is absolutely essential at high loads, it is necessary to have sufficient viscosity during these high temperatures. When specifying this minimum viscosity the factors of shear rate and pressure conditions that are prevalent at the lubricating points must also be taken into account alongside that of temperature
14. Low-temperature viscosity
Engine oil is called upon to play a vital contribution when starting and warming up the engine at low temperatures. In this context several, independent of each other, procedures must be heeded.
First of all, the oil's internal friction must not be too large, so that the crankshaft and the other engine components can break free and rotate or move. The oil must be pumpable, i.e. the oil pump must be able to draw it in and deliver it. In doing so the pump must at no time run idle; the oil must flow from the pan to the sieve to the pump. Air must not be locked in. This helps to support the engine being turned over and the bearing points having oil applied to them immediately (excellent flow behavior, lubrication of the engine).
15. Low temperature-dependent viscosity change
The viscosity specifications at high and low temperatures, which directly oppose the physical characteristics of the oil, result from the necessity to keep the temperature-dependent viscosity changes as few as possible. Engine oils should be able to be used regardless of the particular season of the year and the outside temperature.
16. Viscosity stability
Multigrade oils are capable of fulfilling the low temperature-dependent viscosity changes. If however, these are produced with viscosity index improvers, then care should be taken to ensure that these exhibit mechanical, thermal and oxidative shear resistance. This means that the viscosity of fresh oil should be retained for as long as possible and should not be depleted before the scheduled oil change interval is reached.
Area III - Cleanliness
17. Dispersancy
The insoluble oil residue which is generated during the combustion process and the natural oil residue have to be dispersed and suspended; they must not coagulate and deposit themselves on the engine components, this applies to both particularly hot and cold positions.
18. Detergency
Engine oil must be capable of "washing away" previously deposited sediments to a certain extent and thus achieve a cleansing effect.
19. No ring riding/no ring sticking
Combustion and oil residue, which cannot be borne by the oil, tends to deposit itself in the piston ring grooves, because this is where extremely high temperatures occur. Here however, the piston rings which play a significant role in the engine's operation, can be impaired in their tasks. The piston rings must be free to move at all times.
Deposits on the base of the ring groove or on the back of the ring must not be so strong that the ring tends to "ride"; deposits on the ring or groove sides must not cause ring sticking to occur. Riding or sticking rings lead to a power loss, increased oil consumption, ring/cylinder scuffing and to engine failure as a result.
20. Prevention of hot sludge
The formation of sludge should also be prevented at the highest occurring temperatures under all conditions. In particular this should be observed for diesel fuel engines. If the oil pump is forced to breathe in sludge the lubrication of the engine (oil supply/protection against wear) can no longer be guaranteed.
Beyond this, sludge is not only a blemish, it also hampers any maintenance work to be conducted on the engine, as well as draining oil and carrying out an oil-level check.
21. Prevention of cold sludge
Applies mainly to gasoline engines, but diesel engines that are frequently driven over short distances are also affected and therefore it is necessary that the formation of cold sludge is prevented. Its formation is greatly favored by the presence of condensed water and fuel residue as well as any failure to reach the regular operating temperature.
22. Prevention of paint
Paint, which primarily occurs in gasoline engines after running at high temperatures is also to be prevented where possible.
Paint coats, that exceed specific limits, will impair the operation of engine components. Paint also hampers the heat transfer, heat dissipation is poorer and excessive temperatures are the result.
23. Resistance to water
Condensed water can form at any time and anywhere and succeed in entering the engine oil. This must not be impaired in its quality and function in any way.
24. Resistance to antifreeze with corrosion inhibitor
Coolant (water and antifreeze with corrosion inhibitor) occurs only rarely in engine oil, however in the majority of such cases this can ruin the engine oil and cause sludge to be formed in the engine.
A greater resistance of the engine oil to water and antifreeze with corrosion inhibitor is highly desirable.
Area IV - No residue
25. No deposits on intake valves
Deposits on intake valves cause engines, that in terms of emissions and fuel consumption are ideally set, to malfunction during operation, particularly during the warm-up phase. Although fuel does indeed exert an essential influence it is important to ensure that the engine oil formula does not enable the oil to contribute in any way to the formation of deposits
26. No residue formation in combustion chamber
A certain minimum amount of engine oil is also burnt in the combustion chamber, this must not however generate any residue or deposits. In direct-injection diesel engines the distances between the underside of the valve disk and the top of the piston base is extremely small at specific crankshaft positions. On no account may contact take place as a consequence of any residue or deposits.
27. No glow ignition
When residue is formed in the combustion chamber of a gasoline engine, it can have an affect similar to a glow plug and cause advance ignition and piston scorching. This must be prevented.
28. No deposits in area of turbochargers
Extremely high temperatures can occur close to turbochargers, particularly after switching off the engine. Here and in the entire charge-air cooling system there should be no formation of deposits.
Area V - Oils/engine components
29. Corrosion protection
All metallic engine components must be reliably protected against corrosion, this must also include long service life periods. This requirement applies to all engine oils, in particular of course for break-in engine oils.
30. Compatibility with metals and paints
It goes without saying that engine oils must be compatible with all the various metals that are present in the engine construction and that they are in no way impaired. There have however been no problems in this area for a long time.
The engine oil must also be absolutely compatible with all paints used for the body paintwork, i. e., such paints must not be impaired in any way. Occasionally engine components are also painted on the inside, e. g. the crankcase. These paints too must not be aggravated in any way by the engine oil.
31. Compatibility with elastomers (seals)
Similar requirements regarding compatibility with the elastomers (seals) are also essential factors; the engines must be absolutely tight and remain so. Even the finest engine oil is useless if it does not remain in the engine; leaking oil is never a pleasant sight and is nothing less than environmental contamination. Seals must not shrink or become brittle and crack under the influence of the oil, a slight swelling is normally tolerated. The resistance properties must remain intact. When a new engine oil comes onto the market it must be compatible with all the seals that are installed in the engine.
32. Compatibility with filter materials
Primary and bypass filters or their inserts are made of different materials, e. g. high-grade paper or stuffed cotton. Engine oil must be compatible with all these different materials and provide a trouble-free filtration.
33. No plugging of filters
Naturally, the engine oil itself, and in particular the additives in it, must not lead to the filter being plugged up (increase in differential pressure).
34. Thermal conductivity/cooling effect
It is the task of engine oil to cool the engine components which are the most highly stressed from a temperature point of view, i.e. to dissipate the heat. Obviously the temperature level in the engine is highly dependent on the engine design and operating conditions. Only when the component and oil temperatures do not exceed a reasonable value, is it possible to guarantee a long service life for the engine. To this end the engine oil must fulfill its role as a heat- transfer oil.
35. Sealing capability
Where possible a complete and faultless sealing between the combustion chamber and the engine compartment is a significant precondition for ensuring high degree of engine efficiency. Engine oil must support the piston rings in this task.
Area VI - Basic oils/additives
36. Solubility of additives
All additives used in the production of engine oil must be capable of being completely dissolved in the basic oil and remaining so.
37. Homogeneity
The engine oil must be absolutely homogeneous, even if stored in large containers over a longer period of time and if it has been refilled frequently.
38. No filtering out of additives
Several of the previously mentioned points make it inevitable that the applied additive may not be filtered out.
39. No heat development
The additives do not work solely on account of their presence, but rather their chemical conversion. As little heat as possible should be generated by this process.
40. Foaming prevention
Oil is subjected to very turbulent motion in the crankcase; this gives rise to the possibility of air intake, particularly at very high engine speeds. However, this air intake must be as low as possible in order to prevent any substantial foaming. Oil foam can naturally not form the required lubricating film; as a result wear damage occurs. Similarly, the hydraulic valve-clearance compensation is also impaired, with the result that undesirable noise is heard when the gas content is too high.
41. Air output capacity
However if foam has already formed, the entrained air must be released again immediately, i.e. the entrained air must not be retained.
42. Low volatility/vaporization trend
All combustion engines have a certain degree of oil consumption. As a result the necessity to top up with fresh oil also represents an advantage in terms of the qualitative status of the oil replenishment and consequentially with regard to the wear protection and the cleanliness of the engine. However, no natural oil consumption, dependent on the oil composition, may take place solely on account of the high temperatures. The volatility, i.e. the tendency of the oils to volatize must be therefore be low. This is particularly important with regard to basic oils or basic oil components (multigrade oils) with low viscosity.
Area VII - Application
43. Fuel consideration
The fuel has a considerable influence on the engine oil. This is not just a matter of the different levels of sulfur content in diesel and gasoline fuels. The use of unfavorable and poorly combustible diesel fuel qualities results in a considerable amount of combustion residue in the engine oil.
Nonburned fuel residue reduces the viscosity of the oil. Fuel additives can impair the function of oil additives. Nonburned fuel additives make their way into the engine oil.
Other fuels, such as methanol or plant oil methyl ester can demand modified engine oils. Flexible engines that have been designed to cope with several types of fuel, should also be supplied with corresponding engine oils, that are suitable for all kinds of fuel and mixtures. The suitability of engine oils must be checked completely for all alternative fuels.
44. Miscibility/compatibility
Engine oils, even if from various producers and different SAE areas, must be mixable and absolutely compatible. This also applies to all products that are intended for the same purpose, regardless of whether they, e.g. are based on synthetic or mineral basic oils. Decisive is whether the mixture fulfills all the tasks placed on the engine oil in every mixture ratio. A reference to miscibility on its own is therefore not sufficient.
However its is also obvious that mixtures cannot always be as good as non-mixed oils with regard to all the criteria. Certain losses in terms of viscosity temperature behavior and performance cannot be ruled out.
45. Running-in characteristics
Those engine oils that are used for new or reconditioned engines must, alongside their other tasks, also accelerate the running-in characteristic or at least make it possible.
46. Large change intervals
Oil changes not only cost time and money, but also represent a major organizational task where large fleets are concerned. During the necessary stand-down times the vehicle is not capable of fulfilling its transportation tasks. For this reason, there is now a call for engine oil to not only fully fulfill all of its tasks when new or after only a few thousand driven kilometers, but for it to also do so over as long a period of operation as possible. A "lifetime filling" however still remains an illusion.
47. Applicability in different types of engine (manual transmissions, hydraulic systems)
The idea of developing an optimum oil for each different kind of engine, is only a positive notion at first glance, this applies even to running-in oils. It is much more appropriate, to cater for as many of the various types of engine on the market with as few engine oil versions as possible and to do so not only adequately, but also without any associated problems.
With the great diversity of motor vehicles, resulting from the different requirements placed on these vehicles and from their competitive situations, there are of course a great deal of engine models present that have to be supplied with only a few different oil grades. It is not only the commercial and logistical reasons that compel oil grades to be kept to a minimum, but also the clarity required by both service and workshop operations. The fewer oil grades that are available, the less the danger of getting them mixed up.
In addition to their use in engines there are certain cases where there is also need to use engine oils in manual transmission and hydraulic systems.
48. Constant quality
It is not enough if the demands posed can only be fulfilled by samples manufactured under laboratory conditions. Industrial production or manufactured products must comply with all demands. This is of course only possible with extremely constant production methods. Unavoidable production tolerances must not lead to any losses of quality. The finest development is worthless if it cannot be produced constantly in the desired quantities.
49. Inexpensive manufacturability
The optimum engine oil formulation must also undergo inspection as to whether it can indeed be manufactured inexpensively. There must be an appropriate relationship between price and quality.
50. Availability
Engine oils approved by MB should be available worldwide if possible. This particularly applies to the so-called Low SPAsh oils necessary for vehicles with diesel particulate filter.
51. Storage life
On the condition that storage has taken place properly, i.e. good container, no ingress of contaminants and water, practically unlimited shelf life is to be claimed.