Synthetic Oil Vs High Mileage: Which is the BEST for your Car?

When it comes to choosing the right oil for your vehicle, the market offers a wide range of options. Two popular choices are synthetic oil and high mileage oil.

Both of these oils have specific formulations designed to address different needs and conditions.

Synthetic oil is a type of oil that contains artificially made chemical compounds. They can also be manufactured using chemically altered petroleum compounds instead of just using crude oil.

On the other hand, high mileage oil is designed to specifically deal with the problems experienced by high mileage vehicles (in most cases above $75,000). High mileage oil will reduce smoke, emissions, and high oil consumption from old engines.

What is Synthetic Oil?

Synthetic oil is a type of lubricant that is specially engineered through chemical processes to offer superior performance and durability compared to conventional mineral-based oils.

It is designed to provide enhanced lubrication and protection for various types of machinery and engines, including automotive engines, industrial equipment, and aircraft engines.

Synthetic oil is made using a base oil, which can be derived from petroleum or synthesized from other chemical compounds.

The base oil is then modified and combined with a range of additives to enhance its properties. These additives can include antioxidants, detergents, dispersants, viscosity modifiers, anti-wear agents, and corrosion inhibitors, among others.

The manufacturing process of synthetic oil involves refining and purifying the base oil to remove impurities and undesirable components.

This results in a more consistent and stable oil with a higher level of performance characteristics compared to conventional oils. Synthetic oils typically have a more uniform molecular structure, which allows them to maintain their viscosity and provide better lubrication across a wider temperature range.

Synthetic Oil Vs High Mileage

Advantages of Full Synthetic Oils

Full synthetic oils offer several advantages over conventional and synthetic blend oils. Here are some of the key advantages of using full synthetic oils:

Superior engine protection

Full synthetic oils provide excellent lubrication, reducing friction and wear on engine components. They have a higher viscosity index, which means they maintain their viscosity and protective properties better across a wide range of temperatures. This helps to minimize engine wear, extend engine life, and improve overall performance.

Enhanced temperature resistance

Full synthetic oils have better resistance to high temperatures compared to conventional oils. They can withstand extreme heat without breaking down or thinning out, which is especially beneficial in demanding driving conditions or during heavy towing.

Improved fuel economy

Synthetic oils have lower internal friction and reduced drag compared to conventional oils. This reduced friction leads to improved engine efficiency and can contribute to better fuel economy. While the difference may not be dramatic, using full synthetic oil can help maximize your vehicle’s fuel efficiency potential.

Longer oil change intervals

Full synthetic oils typically have better resistance to oxidation and thermal breakdown, allowing them to last longer before needing to be changed. While oil change intervals vary depending on the vehicle and driving conditions, full synthetic oils generally provide extended drain intervals, which can save you time and money in the long run.

Better cold-start performance

Full synthetic oils flow more easily at low temperatures, even in freezing conditions. This improves cold-start performance and provides better protection during engine startup when most wear occurs. Synthetic oils also reach critical engine components faster, reducing engine wear and improving overall longevity.

Reduced sludge and deposit formation

Synthetic oils are more resistant to the formation of sludge, varnish, and deposits compared to conventional oils. Their superior detergent and dispersant properties help keep the engine clean by preventing the buildup of harmful contaminants. This leads to cleaner engine internals and helps maintain optimal engine performance over time.

Compatibility with modern engine technologies

Full synthetic oils are formulated to meet the requirements of modern engines, including those with turbochargers, direct injection, and variable valve timing. These advanced engine technologies can place higher demands on oil, and full synthetic oils are designed to deliver the necessary protection and performance.

What is High Mileage Oil?

High mileage oil, also known as HM oil, is a type of motor oil formulated specifically for vehicles with higher mileage. It is designed to address the unique needs and challenges of older engines that have accumulated significant mileage, typically exceeding 75,000 miles or more.

The key difference between high mileage oil and conventional motor oil lies in its additives and viscosity. High mileage oil contains a blend of additives that help rejuvenate and protect aging engine components, which may have experienced wear and tear over time. These additives often include conditioners, seal swell agents, detergents, and antioxidants.

The conditioners in high mileage oil are intended to revitalize aging seals and gaskets, which tend to deteriorate and become less effective over time. By rejuvenating these components, the oil helps prevent oil leaks and maintain proper engine performance.

Seal swell agents, on the other hand, work to swell and soften seals, reducing or eliminating oil leaks caused by shrinking or hardened seals.

Detergents in high mileage oil are formulated to clean and remove sludge, deposits, and other contaminants that may have accumulated inside the engine due to extended use. This helps improve engine cleanliness and prevent clogging of vital components.

Antioxidants in the oil help protect engine components from oxidation and degradation, which can be more prevalent in older engines.

In terms of viscosity, high mileage oils are often formulated with a slightly higher viscosity compared to regular motor oils. This helps compensate for potential engine wear, providing better lubrication and protection.

It’s worth noting that high mileage oil is not a requirement for all vehicles with higher mileage. Many modern vehicles can continue to use conventional motor oil without any issues. However, high mileage oil can offer additional benefits and increased protection for older engines that may be experiencing some age-related challenges.

Does High Mileage Mean Above 75,000 Miles?

In reality, there is no “one-size-fits-all” response to this question. As stated previously, 75,000 miles (or 121,000 kilometers) is the average threshold for a “high mileage” vehicles, which is true for the majority of engines.

However, there aren’t precise guidelines for determining whether a vehicle has significant miles. Some experts argue that a vehicle with over 45,000 miles is regarded to have excessive mileage, and that with regular maintenance, a vehicle’s life expectancy is about 200,000 miles. In contrast, ordinary road cars equipped with current technology are capable of traveling up to 400,000 kilometers.


We are all aware that driving in the city differs from driving on the highway.

The consumption of gasoline and the wear and tear on the engines vary. In regards of engine wear & tear, highway miles are much less demanding than city miles, according to various studies.

Simply explained, when driving on highways, the engine maintains a constant temperature, functions at full efficiency, and starts and stops less frequently. In contrast, city miles necessitate many and frequent changes in the engine’s performance mode. This shows that engines with 75,000 city miles may be as worn as engines having 150,000 highway miles.

Obviously, there are other additional factors involved here, such as:

the manner in which the vehicle was driven, the kind and grade of gasoline and oil used, the frequency of maintenance, etc.

In light of these considerations, you must determine whether or not it’s time to begin using high-mileage oil for your engine’s condition.

Although some motorists wait until 200,000 miles, and others as earlier as 80,000 miles, the average motorist should change to high mileage oil after 100,000 miles.

Advantages of High Mileage Oils

These oils offer several advantages compared to conventional oils, especially for older vehicles with worn engine components. Here are some of the advantages of high mileage oils:

Enhanced Seal Conditioning

High mileage oils typically contain additives that help rejuvenate and condition engine seals. Over time, engine seals can shrink and become brittle, leading to oil leaks. The seal conditioners in high mileage oils can help restore the flexibility of the seals, reducing leaks and oil consumption.

Reduced Oil Consumption

Older engines tend to consume more oil due to increased clearances between moving parts. High mileage oils often have a higher viscosity or thicker consistency, which can help reduce oil consumption by minimizing oil evaporation and leakage.

Improved Wear Protection

High mileage oils typically contain additives that provide improved wear protection. These additives form a protective film on engine components, such as piston rings and cylinder walls, reducing metal-to-metal contact and minimizing wear. This can be especially beneficial for engines with higher mileage, where wear may be more pronounced.

Detergent and Dispersant Properties

High mileage oils often have higher levels of detergents and dispersants. These additives help clean and remove deposits, sludge, and varnish that can accumulate in older engines. By keeping the engine internals clean, high mileage oils can improve engine performance and prolong the engine’s life.

Anti-Foaming Properties

Some high mileage oils are formulated with anti-foaming agents. Foam can reduce the effectiveness of lubrication and cause engine components to wear more quickly. Anti-foaming additives help prevent foam formation, ensuring proper lubrication and reducing wear.

Compatibility with Older Engines

High mileage oils are designed to be compatible with older engine technologies, including those with flat-tappet camshafts. These oils provide the necessary lubrication and protection for engines that may not meet the latest specifications.

Enhanced Heat Resistance

High mileage oils often have improved heat resistance properties. Older engines may run hotter due to reduced cooling efficiency over time. High mileage oils can withstand higher temperatures without breaking down, ensuring reliable lubrication even under extreme conditions.

Is Full Synthetic Oil Good For High Mileage Cars?

Yes, full synthetic oil is often recommended for high mileage cars because it can help protect engines from wear and tear.

Full synthetic oil also has superior cleaning power, which can help keep engines clean and running smoothly.

However, it is essential to consult your mechanic or car owner’s manual to ensure that full synthetic oil is the right choice for your car.

It’s also important to note that there’s been a myth that full synthetic oil is unsuitable for old or high mileage cars. The myth is highly rooted in the idea that the oil is slipperier and incompatible with seals, meaning that it will leak in areas where traditional motor oil won’t leak.

High Mileage Vs Conventional Oil

The debate between high mileage and conventional oil has been ongoing for quite some time. There are pros and cons to both types of oil, and it really depends on your specific needs as a driver needs  to decide which is right for you.

Conventional Oil High Mileage Oils
Conventional oil is the most common type of motor oil used in vehicles. It’s made from petroleum and typically lasts for about 5,000 miles before it needs to be changed.


High mileage oil is a type of motor oil designed for vehicles with over 75,000 miles on their odometers. It’s made with special additives that help protect older engines and improve their performance.


Many people believe that high mileage oil is the better choice for their vehicle, but there are pros and cons to using both types of motor oil.

If you’re driving a lot or have an older car, this could be a good option for you. However, it can be more expensive than conventional oil.

Conventional oil, on the other hand, is less expensive but doesn’t usually last as long. It’s a good option for newer cars or if you don’t drive very often.

When You Should Start Using a High Mileage Oil

While there is no strict rule on when you should start using high mileage oil, it is generally recommended to consider making the switch once your vehicle reaches the 75,000 to 100,000-mile mark. At this point, your engine may start experiencing age-related issues that high mileage oil can help mitigate.

However, it’s important to note that not all older vehicles require high mileage oil. If your engine is in good condition, doesn’t consume excessive oil, and doesn’t have any noticeable leaks, sticking with a conventional or synthetic oil may still be suitable. Regular oil changes and proper maintenance are crucial regardless of the oil type you choose.

Does your car leak oil? If so, it may be time to switch to high-mileage motor oil.

Using high mileage oil in your high-mileage car is one of the most important factors in maintaining the engine’s health over time. These oils differ from conventional oils in that they consist seal enhancers and specific compounds that can reduce internal and exterior engine oil leaks.

To minimize oil leaks and oil burning (which frequently occurs in older engines), experts recommend using high-mileage oil that causes the o-rings, gaskets, and seals of your engine to enlarge.

High mileage lubricants are meant to benefit high mileage engines, often those with over 75,000 miles on the odometer. And while the decision to switch to high mileage oil beyond this mileage is entirely up to the vehicle owner, many experts strongly advise you to do so.

Final thoughts

Choosing between synthetic oil and high mileage oil depends on several factors, including your vehicle’s age, mileage, and manufacturer recommendations.

Synthetic oil offers superior lubrication, extended oil change intervals, and improved performance for newer vehicles.

On the other hand, high mileage oil is specifically designed to address issues associated with older engines, providing protection and rejuvenation. Ultimately, make an informed decision based on your vehicle’s specific needs, ensuring optimal performance and longevity.


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