How Long Does Synthetic Oil Last? (Months & Miles)

Since its inception in 1929, synthetic oil has found its way from fueling war jets to mainstream vehicles. Conversion to synthetics has become most apparent in the last three years, with more than two-thirds of new cars having full or blended synthetic oil requirements. Because of this influx, ascertaining how long does synthetic oil last has grown increasingly important.

So, how long does synthetic oil last? On average, synthetic oil lasts about 6 months to 1 year or 7,500-10,000 miles before needing replacement. However, this is only an approximation and is subject to change based on several factors such as oil brand, age of the vehicle, and driving conditions.

Your service manual should be able to answer the query “how many miles does synthetic oil last?” as well as provide you interval schedules. However, manufacturer recommendations do not always represent real-life situations. That said, continue reading this guide for its take on helpful tips and recurrent discussions surrounding the longevity and dependability of synthetic oil variants.

Measuring Oil Life

“How long does synthetic oil last?” Like queries tires to use and how to turn off Check Engine Light, this seems to be part of the list of perennial questions from both new and experienced vehicle owners.

Nowadays, the 3,000-mile oil change rule no longer cuts it for all vehicles, especially recent-year models that utilize synthetic oil blends. Unlike mineral-based engine oil, synthetics have properties that reduce friction and dirt and improve engine performance. Furthermore, these benefits make synthetic oils last longer than conventional ones – and this is more than good news for the frugal car owner.

As if this were not enough, top-notch automakers like Jaguar and Mercedes-Benz have designed their automobiles to stretch oil longevity by up to 15,000 miles. Bear in mind, though, that these figures are based on ideal conditions and could immediately change if one of several facets impacting vehicle use alters. This article will discuss these factors in greater detail.

Does Synthetic Oil Last Longer?

While conventional oils have an interval of up to 6,000 miles between changes, synthetics have improved this by another 4,000 miles on average. And as observed by savvy consumers and mechanics, the brand plays a part in the longevity of synthetic oils or oil blends. For example, European formula Castrol (view on Amazon) Longlife reportedly lasts up to 20,000 miles.

In truth, the answer to “how long does synthetic blend oil last?” actually depends on the type of synthetic oil in question. Consumers currently have two options – this and a full-synthetic type. When comparing the two, full-synthetic oils last longer than synthetic blends (view on Amazon) – more so when compared to purely conventional or mineral oils.

Based on test results conducted by the American Automobile Association (AAA), synthetic oils (full and blended variants) outperformed conventional oils in cold-temperature pumpability, deposit formation, oxidation resistance, shear stability, and volatility. All these facets contribute to prolonging the good condition of synthetic oils before the need for an oil change arises.

In the case of two full-synthetic oil variants, determining which is superior boils down to the primary synthetic composition of the given oil. Different brands make use of multiple synthetic types – each with a distinct set of properties. Polyalphaolefins (PAO), which share the same chemical makeup as mineral oils and is common in most vehicles, is just one of them.

The Truth Behind Longer Oil Change Intervals

Unknown to many, using synthetic oils is not the sole basis for longer oil change intervals. How long does a synthetic oil change last also rides on other equally significant factors, as stated below:

Viscosity Index

One irrefutable fact about synthetic oils is that they are more thermally stable than conventional/mineral-based oils. While viscosity grade has the same effect on the latter, synthetics are generally better and last longer as they are more resistant to breaking down under extreme temperatures. Additionally, they contain additives that reduce sludge and slow down viscosity loss while improving wear protection.

Type of Engine

Premium synthetic oil does not guarantee the same longevity for all types of vehicles. Using full-synthetic oil on gas-fed and diesel-fed engines will render different results. Compared to gasoline, diesel is less refined and produces more soot and acidic by-products. These contaminants take away from how long full-synthetic oil lasts, even when using premium synthetic oil brands.

The same is true when comparing standard with turbocharged engines. For regular engines, the spinning stops the moment you turn off the engine. For turbos, they continue to spin for a while beyond engine shut-off. Because it takes longer for turbos or supercharged engines to reduce their spin back to idle, they harbor more high heat in bearing surfaces. High heat causes hydrogen and hard carbon deposits – elements that contribute to more sludge buildup even when using synthetic oil.

Accumulated Mileage

Another case in point is brand-new versus high-mileage engines. Granted that two vehicles have the same kind of engine (either gas or diesel), powerplants with lots of miles under their belt almost certainly have a greater amount of unburnt fuel getting into the crankcase. Again, more contaminants mixed with fresh synthetics mean faster deterioration of the oil’s quality, resulting in more frequent oil changes.

High-mileage vehicles need not necessarily be vintage. You may classify your wheeler as such depending on how you foresee using your car in the future. If you look at your vehicle from this perspective, oil change frequency also works in reverse. Veteran owners observed that long, multi-year change intervals reduce the chances of using a car for more than 400,000 miles. So, if you intend to use your vehicle more often than you would a daily commuter, shorter oil change intervals may be more suitable.

Driving Pattern

Driving styles or behaviors differ depending on lifestyle and partly on geographical location. Farmers would agree that their vehicles are subject to severe service more than normal driving. People who live in crowded cities tend to experience more stop-and-go traffic. In like manner, those located in areas accessible only by Interstate highways are less likely to have roughed up engines.

Manufacturer-recommended oil change intervals largely depend on this aspect. What you typically get from online search results (when asking, “how long does synthetic oil last”) is based specifically on normal driving conditions. Frequent cold starts and short trips reduce useful oil life and warrant different (often shorter) change intervals. So, if you are told to change your oil annually, take this advice with a grain of salt.

Riding Conditions

Even with high-quality air filters, tons of dirt can still get inside your vehicle in very dusty environments. Once this happens, contaminants can pass through and mix with engine oil, causing accelerated oil degradation. Similarly, riding in hot weather can cause excess moisture and metal wear, leading to premature oxidation and engine corrosion. Both scenarios are but part of various riding conditions that adversely affect usable oil life.

Oil Life Monitors

Most cars (especially late-model ones) equip oil life monitors. Oil life monitors (a.k.a. Intelligent Oil Life Monitor System™ in Ford and Lincoln vehicles) are high-tech systems that track driving habits and other conditions, along with mileage, idle time, ignition starts and stops, and trip hours. Based on gathered data, these systems then tell the driver the right time for engine oil replacement.

Depending on thoroughness, some oil life monitors calculate oil change intervals based only on a handful of factors. More sophisticated systems consider so much more, including engine and ambient temperatures, vehicle speed, and a slew of other operating parameters. Although not an absolute, it would be safe to say that the more variables taken into account, the more accurate the readout is.

Regardless of oil life readouts, most manufacturers suggest changing the synthetic oil once per year. And it would make sense to take their word for it. After all, data from oil life monitors are based on computer-generated algorithms and are still considered estimates. Vehicles typically do not have sensors in the oil pan. But for those that do, those sensors are still subject to contaminants and other possible causes of malfunction, leading to inaccurate readings.

Vehicle Care

Many owners leave their cars sitting in the garage during winter, as they believe that starting the engine in sub-zero weather can do more harm than good for their wheelers. If you happen to follow this precautionary measure, I recommend changing the oil every fall before storing your vehicle for extended periods, regardless of mileage. Doing this helps with the longevity of your oil. Not to mention that it ensures you only have contaminant-free oil sitting in the gut of your engine all winter.

Another thing to look into is the state of your oil filters. Oil filters are responsible for keeping all the harmful stuff that makes oil age quicker away from the inside of the engine. Being a key component of your engine’s lubrication system, a poor-quality or incompatible oil filter is going to defeat the purpose of using premium synthetic oil. The same outcome is expected from a bypassing oil filter (even if you intend to prevent oil starvation).

Frequently Asked Questions

• How many months does synthetic oil last? On average, synthetic oil lasts from 6-12 months. Depending on viscosity grade, some synthetic variants are more thermally stable than others and may extend oil life by a few more months. Ultimately, it depends on the different factors discussed in this guide. For comparison, vehicles subject to hard-driving most likely require closer-interval oil changes than those ridden on the freeway.
• Will synthetic oil last 2 years? Several synthetic motor oil brands have claimed extended periods of oil life reaching up to two years. However, this is hardly realistic. An excellent way to know how long your synthetic oil will last is to refer to your service manual and take your driving habits and other vehicle-impacting parameters into account.
• Does refraining from starting your vehicle during winter help prolong oil life? Honestly, there are numerous discussions around this topic, splitting vehicle owners into those who go for and against the idea. But to think that the answer to this question is subjective wouldn’t be entirely correct either.

Determining if frequent cold starts are beneficial for your wheeler is dependent on several factors. These include how sophisticated your engine management system is and whether your car has a carbureted or a fuel-injected system. There is also a thin barrier stopping normal cold starts from becoming cold-start scuffing. Lastly, the age of your vehicle is something you would want to include in your considerations. 

Conclusion – How Long Does Synthetic Oil Last?

Even today, there exists no magical app or calculator where you can just input every variable and get an accurate schedule or a specific number of miles before your next oil change. Vehicles will keep on evolving, and automakers will continue constantly changing their recommendations – be it due to a high rate of mechanical parts failure at low mileage, an increase in long-term repair expenses, or some other reason.

The key to stretching how many months synthetic oil lasts and making the most of using this type of oil is to be in the know. Anyone can do this by keeping an eye on TSBs or any other updates about your vehicle’s specific make and model. It’s also beneficial to research newly introduced synthetics in the market. Most importantly, personal preferences should always align with manufacturer recommendations on using conventional versus synthetic oil and change intervals.