Why Do Engines Burn Oil? Understanding the Mechanism and Impact

Oil is a critical component in every engine, serving primary functions such as lubrication, cooling, and protection. Despite advancements in engine design and manufacturing, the issue of oil burning persists. This phenomenon can be perplexing to many vehicle operators, leading to questions about the normality and impact of such occurrences.

Oil Consumption in Engines

The primary purpose of oil in an engine is to lubricate all moving parts, reduce friction, and wear. It is designed to maintain its viscosity and lubricating properties over its life span. However, it is crucial to note that oil is not meant to be burned by the engine. The burning of oil can lead to significant engine damage and performance degradation.

How Engines Consume Oil

Oil consumption in engines can be attributed to a variety of factors. In internal combustion engines, small amounts of oil can seep through the piston rings and into the combustion zone, where it gets burned. This leakage is controlled through specialized oil control rings, but some oil inevitably makes it past these rings.

Similarly, in jet engines, oil may also leak into the gas path, leading to burn-off. This is a common occurrence, although the amount of burn-off is typically minimal and goes unnoticed under normal conditions.

Impact of Excessive Oil Burning

As an engine ages, wear and tear increase, leading to more oil being deposited on the cylinder walls. This accumulation can result in more noticeable oil burn-off. If the amount of burned oil becomes significant, it can unequivocally indicate a severe wear issue in the engine.

Monitoring and Assessing Oil Consumption

Traditionally, the rule of thumb for oil consumption was that 1 liter per 1,000 kilometers is considered excessive, while 500 milliliters is acceptable. Modern vehicles have improved their internal consumption, but some may still consume through their breather systems or experience leaks.

Generally, oil consumption of 1 quart per 1,000 miles is considered excessive by most manufacturers. However, the acceptable range can vary depending on the usage of the vehicle. For instance, taxis or heavily used vehicles may burn more oil due to increased demand and usage.

Modern Engine Designs and Oil Consumption

Modern engine designs, such as those with Variable Valve Timing (VVT), may inadvertently burn a small amount of oil when switching between preset modes. This is particularly true in advanced systems where precise control over engine conditions is necessary.

Regardless of the engine design, all engines consume oil to some degree. However, the amount can vary significantly. Some engines may only consume a teaspoon of oil over several thousand miles, which is generally considered excellent and not easily detectable through dipstick checks.

Manufacturers often set a maximum allowable oil burn rate, typically around 1 liter per 10,000 kilometers, as detailed in the owner's manual. Excessive consumption can indicate more serious internal engine issues.

Understanding the mechanism and impact of oil burning can help owners and mechanics diagnose and address potential engine issues more effectively. Regular maintenance and monitoring can significantly reduce the risk of damaging an engine due to excessive oil consumption.