The oil consumption of a combustion engine can become a very touchy subject between the customer and the workshop, particularly then, when it comes to fulfilling the terms of a guarantee. Although the calculated consumption is correctly given in liters per 1000 kms, in the practice it's very difficult to determine without leaving room for doubt. Thereby, one should first of all exclude the possibility of oil-loss. This, by the way, can easily be seen on the garage-floor or on one's parking space, indeed, there are also stubborn cases, where the loss only occurs while driving.

The manufacturers nowadays, give the oil consumption to be 0,6 to 1 liter per 1000 kms, which of course, for a modern vehicle, is a gross exageration. Indeed, there is a reason for this information, it protects the manufacturers from excessive guarantee claims. In the past these were only possible values, the amounts recommended in the owner's manual were even higher. Those were the times when any sort of engine problems were diagnosed by having a higher oil consumption.

The oil consumption can always be 'adjusted'. E.g., through the pre-tension of the piston's oil-rings. To put it simply, the pressure of the rings against the sleeve is increased until the targeted performance can no longer be attained. It is then reduced again so that, per stroke, a little less oil is scraped off, thus reducing the amount which reaches the crankcase. You may have noticed that so-called used oil has made it's way into the crankcase, where it is burnt off. Apart from that, also from the aspect of emission values, are the manufacturers interested in keeping the oil consumption down.

So, over the years the times have changed. In the past, when the car was new, which was also the main guarantee period, the largest amount of oil was consumed. Since before, e.g., the grooves from the honing had been smoothed out, quite a lot more oil was used. This situation was often an important part of the dialogue between the workshop and the customer. The workshop argued, that one should wait until after the running-in period before judging, the customer on the other hand, was afraid that he was being delayed until after his guarantee had expired.

After all, the risk could mean substantial costs. Should an older car tend to use more oil, one could still hope that it was only faulty shaft-seals. In the case of newer engines this can almost always be excluded. Thus, the engine must be removed and opened and in many cases a replacement engine could be the better solution. This makes it easy to understand, why the disputes were carried out so passionately. The question remains, whether such conflicts are even possible nowadays.

The construction methods in the high-volume production series have changed. For example, the cylinder-sleeves nowadays have been processed so that far less running-in time is necessary. Although it's quite clear, that an engine must use a certain amount of oil, the amount that has to be topped up has been drastically reduced. 30.000 kms without adding a single drop is not unusual. In this case, we are of course, speaking of a motor car engine, whereby a gentle driving manner is assumed. Should the engine be hammered, this can lead to a very different result indeed.

Nevertheless, complaints are still possible. How do the big manufacturers handle them? With the help of computers of course, and the unconditional striving for objectivity. After a detailed examination of possible leaks has been made the oil consumption is very precisely determined. Thereby, a sort of driver-profile is used as a template. From now on, the draining of the oil may only take place at an exactly determined running temperature, eg., 85°C. Then, not the amount of oil is measured, rather the weight which is shown on a precision scale.

In fact, even the time taken for the draining of the hot oil, 10 minutes, should always be the same. Only thus, is a precise measuring fairly certain. Of course, during the measuring period of 1000 kms the car is being used by the customer, because manipulation has to be excluded, the workshop must have faith in the integrity of the customer. At least, the dipstick is sealed. As you can imagine, at the the end of the test-period, even if the customer has driven more than 1000 kms, the consumption can be fairly exactly calculated. The ascertained value is the basis for further procedures.

Although here, it must be pointed out, that, e.g., in wintry short distance driving conditions, it may appear that more oil is in the sump. In this case, there is a certain amount of petrol mixed in with the oil. Recently, because of the post-injection, this is even possible in Diesel engines, which was otherwise completely unheard of. One thing is certain, such a mixture is damaging to the lubrication and it does not always disappear through driving for a longer period. In this case, an earlier than planned oil-change has to be carried out. 05/13