Photo: Why You Shouldn't Forget to Change Your Engine Oil (Getty Images) Author: Konstantin Shirokun
There can be many reasons for delaying oil change – as well as consequences. How catastrophic will they be? We tell you what will happen to the engine after running on “expired” oil.
Read about the consequences of running a modern engine on old oil in the RBC-Ukraine article.
It is clear that an instant catastrophe will not happen – the engine will not notice the final calendar date or critical figures on the odometer and will continue to work. But there will certainly be consequences for the unit.
What is old oil
First, a brief overview of what motor oil aging is. Yes, by the end of its intended service life, oil ages. It loses some of its qualities both from age and from the kilometers traveled with the engine (or rather, the hours worked). And there is a whole set of factors that influence the aging process.
Firstly, moisture condensing in the internal volume of a cold, not fully warmed up engine does its evil work: as a result of contact with crankcase gases, it forms acids (nitric, sulfuric, sulfurous). This reduces the alkaline number of the oil, and it loses its protective qualities. Gradually, acids begin to dominate, resulting in the development of corrosive wear of metal engine parts – and so you know, this is one of the main types of wear in modern engines.
In addition, oil that has exceeded its service life has a higher viscosity. This means worse starting qualities in the cold period, and most importantly – the lubrication conditions programmed by the designers are violated. That is, critical parts wear out more intensively.
What is important for the future of the engine is that old oil loses its cleaning additives (this happens partly because of the fuel that somehow gets into the oil). This means that more carbon deposits will be deposited on the parts and they will wear out more intensively.
Differences between cheap and expensive oil
The bad processes caused by oil aging do not start on the same day when the counter starts counting down the oil over-mileage. Its aging occurs gradually, so if the oil itself was cheap and the engine operating conditions were severe, then its degradation will already be, so to speak, in the process at that time. On the other hand, a premium oil may not notice a small over-mileage, since the efficiency reserve of additives in such products is always higher.
What harm does old oil do to an engine?
It is very bad that the dirt left on the parts due to the weak action of the so-called cleaning additives turns into sludge after heating, and the heat exchange between the engine parts and the lubrication of individual friction pairs deteriorate.
Deposits left in critical areas and areas of increased heating – pistons, grooves of their rings – also turn into sludge and varnish-like deposits. They limit the mobility of the rings, compression in the cylinders decreases, accordingly the engine power decreases, fuel consumption and oil consumption itself increases.
In this case, excess oil remains on the pistons and in the combustion chamber, and when overheated (200 degrees C and above), it turns into sludge, and in particularly hot zones – into solid carbon deposits. Which, in turn, acting as an abrasive, contribute to intensive wear of the cylinder-piston group parts. Worn-out cleaning additives of old oil can no longer collect these contaminants and carry them to the filter, so the wear of parts progresses even more.
In brief
So, if you miss the engine oil change deadline, nothing terrible will happen at first. However, each subsequent kilometer and each subsequent engine hour worked by the engine on expired oil will be increasingly deadly for the engine: the resource of the unit will be reduced with an increasing coefficient.
If you are deliberately postponing oil change (there are different situations in life), avoid harmful engine modes: idling, driving under load at too low revs (up to 1800 – 2000 rpm) or, on the contrary, prolonged engine over-revving (above 4000 rpm). If you have to postpone the change in the future, perhaps you will be able to do otherwise – for example, temporarily replace the oil with some inexpensive one? If it corresponds to the quality and viscosity class, it will still be better than winding up the second circle of the interservice mileage on old oil with virtually no additives.
In preparing this article, materials from Autobild, Opet and Liqui Moly were used .
Let us recall that RBC-Ukraine recently reported why pedestrians are not always right.