The Causes of Increased Oil Consumption

Increased oil consumption can be attributed to two main causes:

• Oil leakage – in most cases, oil leakage is present.
• Combustion of motor oil – the oil enters the combustion chamber and burns there.

Here, we refer to the type of oil consumption in which the motor oil burns during engine operation.

The Degree of Oil Consumption

For each vehicle, the engine manufacturer specifies a guaranteed oil consumption level that is considered normal under standard operating conditions. Many assume that zero oil consumption is the norm, but in reality, every internal combustion engine has a minimal oil consumption level.

For engines manufactured around the turn of the millennium or earlier, an oil consumption of between 0.05% and 0.5% of fuel consumption is considered normal under typical use. With an average fuel consumption of 8 liters, this would correspond to 0.4 dl – 4 dl per 1,000 km.

In recent years, vehicle manufacturing technology has advanced significantly, allowing for tighter clearances in engine production, which has led to a substantially reduced oil consumption in modern engines. In a modern vehicle, the normal oil consumption is only 0.05% to 0.1% of fuel consumption, which corresponds to about 0.4 – 0.8 dl per 1,000 kilometers with an 8-liter fuel consumption.

Any consumption exceeding this level is considered an abnormal oil consumption.

The Relationship Between Engine Age and Oil Consumption Causes

Oil consumption generally changes with the age of the engine. A new engine has a so-called break-in phase during which parts wear into each other. During this phase, increased oil consumption may be normal for some engines. Therefore, manufacturers recommend regularly checking the oil level during the first 1,500 to 3,000 km and topping it up if necessary.

After the break-in period, the increased oil consumption decreases to a normal level. As the engine continues to age and accrue mileage, especially toward the end of its lifecycle, oil consumption begins to rise again. This increased oil consumption is often due to mechanical causes.

What Can Cause an Engine to Use More Motor Oil Than Normal?

Increasing oil consumption is not solely due to the engine's age. Numerous other factors influence oil consumption.

• Challenging operating conditions, such as towing, sporty driving, or extended idling, can lead to higher oil consumption.
  
  
• Changes in oil viscosity: Using a motor oil with a lower viscosity can increase oil consumption. For example, switching from 5W-40 to 5W-30 or 0W-30 after an oil change can lead to increased consumption.
  
  
• Lower oil quality: Using inferior, cheap motor oil can also cause higher oil consumption. Modern low-viscosity motor oils evaporate more quickly, and lower-quality oils can evaporate more than premium products even at the same viscosity. Therefore, it is advisable to use high-quality motor oil.
  
  
• Extended oil change intervals can also cause excessive oil consumption. Over time, fuel entering the motor oil can dilute it to the point where its viscosity decreases, causing the engine to consume more oil.
  
  
• Low oil level over an extended period: A permanently low oil level can also lead to increased oil consumption, as the oil is subjected to greater stress during operation, leading it to wear out more quickly and reach the end of its life.

In these cases, engine oil consumption can be relatively easily controlled. However, since the average age of vehicles is already over 15 years according to the latest data, this is not the main issue here. In most cases, increased oil consumption is due to the vehicle's age and mileage, which is neither beneficial for the vehicle nor for the environment.

What is the real reason for excessive oil consumption in many cases?

Most vehicles on the roads were manufactured between 2000 and 2010 and have been in use since then. In that time, an average car has traveled at least 200,000 to 250,000 km under normal usage, and there are also examples with mileages of 300,000 to 400,000 km.

With such high mileage, the condition of the engine primarily depends on whether the vehicle has been regularly maintained. The condition of the engine and the vehicle almost entirely depends on how the owners have used the vehicle, how frequently maintenance has been carried out, and the quality of the lubricants and parts used over its lifetime.

Choosing an overly long oil change interval or using low-quality motor oil can lead to deposits forming in the engine, increased oil consumption, and even irregular wear on engine components.

An oil consumption of 2–3 dl per 1,000 km is considered noticeable and annoying (though still within normal limits). At this rate, during a 10,000 km oil change interval, the entire amount of oil between the maximum and minimum oil level is depleted at least once, requiring more frequent oil checks and regular top-ups. At the upper limit of normal oil consumption, around 1 liter of motor oil would need to be topped up after 2,000 km (about 1 to 2 months of average driving).

Most users are aware that high oil consumption is due to wear and the condition of the engine from age and use. The cost of a complete engine overhaul often represents a significant portion—or in some cases, even the entirety—of the vehicle's value.

Which Oil Does My Car Need?

The oil your car needs depends on the manufacturer's recommendations, which can be found in the owner's manual. It's essential to choose the correct viscosity (e.g., 5W-30 or 0W-20) and any required specifications, as these are tailored to the engine's design. For older vehicles, it’s advisable to use a high-quality oil that meets wear protection requirements.

Why Should We Not Deviate from the Manufacturer's Specified Motor Oil Viscosity?

When deciding on the best oil for our car to reduce oil consumption, we should consider the pros and cons of high-viscosity oils. If we use an oil with a higher viscosity than specified due to high oil consumption or add an oil additive, we may indeed reduce oil consumption, as thicker oil seals better.

However, this means less oil reaches the bearings because the thicker oil flows more slowly through narrow bearing clearances. Additionally, due to the slower flow, the oil is less effective at cooling surfaces, which can lead to increased temperatures in engine parts, more deposits, faster oil aging, and increased engine wear.

Another point is that higher viscosity also causes a slight increase in oil pressure, which can further raise the engine temperature. These factors contribute to a further increase in oil consumption in the medium and long term.

The engineer sets the motor oil viscosity and other oil requirements after careful consideration, which are defined in the oil standards specified by the manufacturer. Even in cases of increased oil consumption, it is not recommended to deviate from these standards, as this could lead to improper engine function, premature wear, and aging. The best motor oil is always the one specified by the manufacturer.