How Often Should You Change Your Engine Oil

Do I have to change the engine oil in my car every year even if I drive very few kilometers?

Many drivers believe that the annual oil change is a ‘trick’ by workshop owners/garages, a maneuver to make money. 

But chemistry and mechanics say otherwise. The oil, even if the car remains stationary, ages. It loses viscosity, oxidises, absorbs moisture and stops fulfilling its essential function, which is to keep the metal parts that rotate at thousands of revolutions separated. 

And then a silent ageing process begins, without immediate symptoms… until one day the engine suffers and starts to ask for ‘help’.

According to the Society of Automotive Engineers (SAE), the mixture of base hydrocarbons and chemical additives is designed to withstand extreme temperatures and pressure, but not indefinite time. 

Oxygen, ambient water and microscopic debris left in the crankcase after the last start-up act as a corrosive cocktail that oxidises the compounds and reduces their ability to clean the engine. Even if the vehicle sits for weeks without moving, internal micro-condensation causes acids to form that attack the metallic parts of the engine.

The danger of short journeys

Engine Oil manufacturers recommends changing the oil between 5,000 and 10,000 kilometres, or once a year, whichever comes first. In cars more than 15 years old, the engine oil brands advises doing it at 5,000. 

You could say that they indicate this because they are an ‘interested party’, but the corroborates this recommendation warning that a year is enough for the additives to lose their effectiveness, especially when the car makes short journeys in which it does not reach its optimum temperature. On these short journeys, the engine does not evaporate the combustion water, and this moisture is trapped in the oil, degrading it beyond repair.

100% synthetic lubricants, which are the so-called group IV or V according to the API classification, better withstand the passage of time thanks to lower oxidation. Even so, producers like TotalEnergies and Repsol warns that even these high-end oils should be replaced every year if we leave the car parked for a long time. The French company sums it up with a phrase that sounds like a slogan: “Oil does not age so much by miles as by conditions”.

In addition, it turns out that today’s more efficient, tighter-tolerance engines are more vulnerable to degraded oil. Turbos, start-stop systems and variable valve timing require immediate and stable lubrication. 

So when the oil has lost its ability to maintain pressure or its flow point, those parts suffer. And in hybrid cars the problem is exacerbated, because the combustion engines run in bursts and spend long cold intervals, which often prevents the oil from reaching an adequate and constant temperature. In the words of an SAE engineer, “the hybrid car does not travel fewer kilometers, but its oil ages faster”.

Research has shown that synthetic oil degradation reveals that after 12 months of very little use of the car, the level of oxidation increased by 40%, and the alkaline reserve (the ability to neutralize acids) fell by 35%. This is equivalent to driving with a lubricant that has already lost half of its useful life, making time (and not the road) the real enemy of the engine.

So, keep your car’s engine healthy and change the engine oil ….. sooner than recommended.