Replacement of engine oil – expert tips

The basic rules that should be observed by mechanics is to replace the engine oil and filters in accordance with the recommendations of a car producer. In case of the air and fuel filters, this frequency varies between 30 and 40 thousand kilometres. For every replacement of the engine oil, it is necessary to replace the oil filter and compartment filter. On the other hand, in the case of diesel and petrol cars, it should be replaced at least every 30 thousand kilometres or every two years. Why every two years? The reason is prosaic: even a short-distance engine will not get warmed up to a working temperature of 90 degrees.

The engines unheated due to faulty thermostats or travelled short distances cause a shortened life span. As a result of the unheated engine, steam condensates, from which water deposits and stays in the oil pan, which in turn results in deterioration of the quality of the oil and inadequate lubrication of the engine. In extreme cases, it can lead to blurring of the turbocharger or the engine. This problem cannot occur in newer cars, i.e. above 2005, because they have a level sensor and an oil quality sensor that will respond and inform the user of the poor quality of the oil. Whereas older cars do not have such a sensor.

You can also meet the opinions that come down to the statement that “Oils need to be replaced more frequently, even at 15, 20 thousand kilometres”. Don’t you agree with this? Yes and no, because in addition to the time from the “replacement to replacement”, the conditions in which the engine is running or whether it has a heavy load, whether it is working in urban conditions or rather on long routes, or in a dusty environment are relevant. For example, the engine of an off-road car operates in difficult conditions, thereby covering small but large and extreme distances. Therefore, in this case, the engine oil should be replaced at least once a season.

Synthetic, semi-synthetic or mineral?

In spite of the years of operation and ageing of the car, if the engine “does not take” the oil and has been primed with synthetic oil, synthetic oils (0W40, 5W30, 5W40) should still be used. In the case of leaks – the case is obvious: seal the engine. If it starts to take the oil, then use semi-synthetic oil unless we choose to repair the engine. Taking the oil by the engine indicates that it is already heavily depleted or has been overheated in the past.

Choice of the engine oil a used car

One of the most common problems is to decide on the choice of the engine oil at servicing of a used car. Particularly, if we do not know precisely its history of previously used oil. Then, follow the course of the car and the technical condition of the engine. The course of approx. 200-250 thousand kilometres indicates the use of synthetic oil of a viscosity grade of 5W40. We should also consider that mechanics, especially older people, are unjustly convinced that if the car has such a course, semi-synthetic oil should be used. The fact is that such preventive action through the use of semi-synthetic oil does not pose a risk to the car. However, if the engine does not take the oil, and it operates properly, then synthetic oil will be used all the time, not suggesting only the state of the meter or mileage.

The basic rule is not to pour the oil (synthetic or semi-synthetic) into the engine if semi-synthetic oil has been previously used. If this is done, it is very likely that the engine will be unsealed or the oil will burn. Therefore, it is important to remember to use the sequence of the oil used throughout the entire life cycle of the car: synthetics, semi-synthetic and only at the end, after a long run and a significantly reduced engine condition – mineral.

However, if there is a mistake in selecting the oil, then the only thing left to us is the observation of the engine operation and checking the oil level for several hundred kilometres. At the same time, we still have to quickly replace the oil with semi-synthetic one.

In the case of the turbocharged engines, it will be the best to pour synthetic oil throughout the engine life. Now, the turbocharger needs this oil after starting the engine as soon as possible. The thinner the oil, the faster it will be delivered, which will ensure the rapid formation of the oil film. Therefore, 10w40 and 15w40 oils are not recommended in this case. The worst effects can occur at -30-40 degrees Celsius, where 15W40 oils are very dense and it can happen that immediately after start-up of the turbocharger, it will not be able to lubricate.

Dedicated oils with the standard

There is also a group of engines, for which the oil must be of a suitable standard. For example, special 50501 standard is dedicated to the Volkswagen engines. If they have the particle filter, then standard 50700 is assigned. Therefore, you should use dedicated oil, e.g. 5W30 but with the standard indicated by the producer. Each car producer has specified its requirements for the engine oils standard.

We will talk about the replacement of the filters in the next part of the article.

Source: Marcin Budziewski in cooperation with Robert Rak and Andrzej Majka.