Should I use thicker oil in a high mileage engine?

As your odometer steadily climbs and your loyal vehicle accumulates the wear and tear of countless journeys, a pertinent question arises: Should I use thicker oil in a high mileage engine?

The choice of engine oil plays a crucial role in maintaining peak performance, especially when it comes to high-mileage engines.

The viscosity of engine oil, whether thick or thin, has a direct impact on how well it lubricates the engine components, protects against friction, and manages heat.

Let’s dive into the intricacies of high mileage engines, and the potential benefits and drawbacks of thicker oils.

Most importantly, a guide through making informed decisions that contribute to sustaining the optimal performance of your reliable vehicle over the long term.

An image illustrating should i use thicker oil in high mileage engine
Should I use thicker oil in high-mileage engines?
Photo credit: amsoil

What is Oil Viscosity?

Oil viscosity is the measure of a fluid’s resistance to flow, or in simpler terms, how thick or thin it is.

The viscosity is usually represented by a number with a “W” for winter, followed by another number (e.g., 10W-40).

The first number denotes the oil’s flow in cold temperatures, while the second number represents its flow at high temperatures.

What Is Thicker Oil?

When you’re purchasing engine oil, the storekeeper will ask you about the oil’s number.

There are options like 10, 20, 30, and 40. These numbers indicate how thick or thin the oil is.

A higher number means the oil is thicker or more viscous.

Choosing between 5W30 and 5W20 synthetic oil means opting for a difference in thickness.

The 5W30 is notably thicker compared to the 5W20.

Images showing different oil vicosities for High mileage engines
Engine oil viscosity
Source: mechanicbase

Benefits of Using Thicker Oil

Using thicker oil in your engine can offer several advantages, including:

  1. Enhanced Engine Protection: Thicker oil forms a more robust protective barrier between engine components, reducing wear and tear. This is particularly beneficial in high mileage engines or those operating under heavy loads.
  2. Improved Lubrication at High Temperatures: Thicker oils generally maintain better viscosity at high temperatures, ensuring consistent lubrication even in demanding conditions. This can be crucial for engines that tend to run hot.
  3. Reduced Oil Consumption: Thicker oil tends to have lower volatility, meaning it is less prone to evaporating. This can result in reduced oil consumption and the need for fewer top-ups between oil changes.
  4. Better Sealing and Reduced Leaks: Thicker oil can improve the sealing properties of gaskets and seals, potentially reducing the likelihood of oil leaks in older engines with worn seals.
  5. Enhanced Film Strength: Thicker oils frequently exhibit a stronger film strength, offering additional protection to critical engine parts, particularly in situations with increased friction.
  6. Suitability for High Mileage Engines: In some cases, high mileage engines with greater internal clearances may benefit from the higher viscosity of thicker oil to maintain proper lubrication.

Should I Use Thicker Oil In a High Mileage Engine?

Yes, You should use thicker oil in a high mileage engine.

In this situation, you’ll see that both 10W30 and 10W40 synthetic engine oils are the right choices.

These two are the top picks for thicker engine oils, ensuring your engine runs smoothly for a long time.

Furthermore, thicker engine oil is consistently a more suitable choice for high mileage engines, as it can withstand increased loads and temperatures.

Using an oil that falls short in supporting your car’s engine could lead to higher overall costs.

Hence, opting for thicker oil remains the optimal choice for a high mileage engine.

Is Thicker Oil Better for High Mileage Cars?

Yes, thicker engine oil is better for high mileage cars.

As engines rack up mileage, the wear and tear can result in expanded gaps between engine components.

Thicker oil can help sustain oil pressure and fill widened clearances, potentially diminishing engine noise and improving protection against wear.

Is Thicker Oil Safe For Car Engines?

Yes, Thicker engine oil is only safer for cars with high-mileage engines.

However, using really thick oil in a regular engine can harm it by causing some problems with how it runs.


The decision to use thicker oil in a high mileage engine is a nuanced one.

Balancing the benefits of enhanced protection against wear and tear with the potential drawbacks of decreased fuel efficiency.

It’s important to note that while thicker oil has its advantages, it may not be suitable for all engines, and the manufacturer’s recommendations should be considered.

Always consult your vehicle’s manual and consider the manufacturer’s recommendations to ensure you make an informed choice tailored to your engine’s specific needs.

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