Can synthetic oil be used in an old car engine?

Synthetic engine oil resists chemical degradation much better than traditional lubricants. It also usually has a higher viscosity index, allowing it to protect engine components from friction better during extreme heat, extreme cold, and everything in between. But will the old engine withstand it?

Slash Gear wrote about this.

Benefits of synthetics

The exceptional stability and low volatility of fully synthetic oils, which contain artificial chemical compounds, provide a longer service life. Some oils exceed 16,000 km between drain intervals.

Although synthetic motor oil can cost two to four times more than conventional oil, the benefits are worth the investment. This explains why nearly 70% of new cars sold in 2019 left the factory with synthetic oil in their engines for the first time.

It is more important to follow the manufacturer's recommendations on oil viscosity and oil change intervals than to choose between synthetic and conventional oil. Refer to the operating instructions to do this.

Also read:

Lexus reliability: how long do Lexus cars last?

7 most reliable diesel engines on used cars

Is there any harm to old engines?

The first synthetic motor oils, introduced in the 1970s, were formulated with chemical compounds that helped clean engines by removing contaminants and sludge — key factors in maintaining performance and efficiency. They also softened and lubricated rubber seals, improving their flexibility.

However, with prolonged or excessive use, these oils sometimes caused the seals to swell and eventually leak. This led to the widespread belief — now largely outdated — that synthetic oil was incompatible with older engines.

Modern synthetic oils are formulated without compounds that harm engine seals or components. In fact, manufacturers like Porsche recommend multigrade synthetic oils even for classic models such as the 911, 914, and 356.

There are also synthetic oils specifically designed for vehicles with over 120,000 kilometers. These formulations include additives that help fill microscopic cracks in metal surfaces, improving engine smoothness and longevity. They also contain detergents to prevent sludge buildup. The only downside is the higher price — but the long-term benefits often justify the investment.

Also read:

Which car engine is better: turbocharged or naturally aspirated?

Why car blind spots are increasing every year?