Astra
|
Oil Consumption, Measure
Oil consumption in an internal combustion engine is defined as that quantity of oil which is consumed as a result of the combustion process. Under no circumstances must oil consumption be equated with oil loss, which occurs when there are leaks in the oil pan, valve cover, etc.
The function of the engine oil is:
a) to separate, by means of an oil film, surfaces which slide against each other, i.e. to prevent dry friction: b) to conduct away heat resulting from friction: c) to conduct away combustion residues.
These functions necessitate a certain oil consumption. The expectation often raised as a result of further development of the internal combustion engine, that an engine uses no oil, is completely erroneous. Operating conditions, driving habits and manufacturing tolerances have a certain influence on oil consumption. Normally, however, this consumption is so small that it is not necessary to add oil, or to add only a small amount, between the prescribed oil changes. It is, however, essential to add oil when the oil level measured on the dipstick has dropped to the "Add" mark. On the other hand, one must ensure that the oil level is not above the dipstick mark, as this would lead to excessive oil consumption.
Since oil consumption is a technical requirement, discovering that an engine uses no oil at all indicates that oil dilution is being caused by certain operating conditions. With frequent cold starts, driving with a cold engine, etc., the oil flowing back into the pan carries with it various low volatility fuel fractions and condensates, which thin the oil and lead to the erroneous assumption that the engine uses no oil. Such diluted oil looses its lubricating properties and can result in damage to the engine if the prescribed oil change intervals are not maintained. A preponderance of city driving and frequent low-speed driving with a cold engine can be cited as the main causes of oil dilution.
As oil consumption stabilizes only after a few thousand miles/kilometres of driving, reliable results from measurement of oil consumption can be obtained only after approx. 4,500 miles/ 7,500 km of operation. Measurements are to be based on weight, as oil volume is dependent on temperature and can thus give false readings. Before making oil consumption tests, ensure that the engine is not losing oil through leaks.
Oil Consumption Measurement
Method I
1. Run engine up to operating temperature (coolant approx. 80° C/176° F and engine oil 60° to 80 °C/140 to 176 °F.
2. Drain all old engine oil from the oil pan.
3. Fill engine with new engine oil: Example 2.25 kg/4.95 lbs. equals 2.5 litres/0.55 gal.).
4. Drive vehicle 300 or 600 miles (500 or 1,000 km) under normal operating conditions. During this time no oil may be added. Then drain the engine oil warm and weigh. The difference between the quantity filled and the quantity drained represents actual oil consumption in kilograms, for the distance driven.
To convert the weight (kg) into volume (litres), the difference in weights is to be divided by the specific gravity for engine oil = 0.9.
Method II
Measurement of oil consumption is even more precise when the vehicle is driven, without adding oil, until the oil level has fallen to the lower mark ("Add") on the dipstick.
It is then possible to calculate for the quantity of oil drained and weighed, compared to the distance driven - as in Method I after 300 or 600 miles (500 or 1,000 km), and then to convert for a standard distance of 60 to 600 miles (100 or 1,000 km). The greater measurement accuracy previously mentioned is based not only on the greater distance driven, but also on the fact that experience shows that with oil at the "normal level" (at the "Full" mark), the first half litre is used more quickly than at lower initial oil levels.
Method II for measuring is always to be given preference over Method I (measurement after 300 or 600 miles/500 or 1,000 km) whenever possible.
|
