Synthetic oil is often touted as needing less frequent oil changes, and while many modern engines actually recommend using it, those of us with older vehicles are often left mystified as to just how often we need a change.
Thankfully, it’s pretty simple to figure out if you’re willing to learn. Let’s take a look at just how often you’ll need to change the synthetic oil in your engine and discuss why these oils last so much longer than their conventional counterparts.
Debunking the 3,000 Mile Myth
It’s commonly asserted that motor oils need to be completely changed out every 3,000 miles in all vehicles.
It’s also wrong.
Especially within modern vehicles, this pervasive myth seems to exist mostly to get you into the local shop much more frequently than you need to be. It’s advantageous to oil manufacturers, the automotive repair industry, and retailers but not to the end consumer. It’s gotten to the point where some nations are trying to educate their citizens that it’s unnecessary.
In fact, most modern vehicles, even with conventional oils, can run up to 5,000-6,000 miles before they need to have an oil change. This is due to both the increased prevalence of better oils, and advances in engine technology as the years have gone on.
These days, even 10,000 miles isn’t all that uncommon. Instead of relying on the people you pay to change your oil and filters, the best thing you can do is consult your owner’s manual to ensure you’re not changing your oil more often than you need to.
It’s easier on both your wallet and the environment, since in many areas a lot of “recycled” waste oils end up just being burnt for furnaces and other destructive applications which doesn’t actually end up reducing the need for oil overall.
Modern Vehicles and Oil Change Intervals
As more and more automotive manufacturers move towards synthetic oil being recommended right from the outset, the oil change intervals within the user manual are quite often about right.
There are some conditions where you may need to change your oil more frequently, generally known as “severe” conditions but it can be pretty hard to figure out if you fall into that category since most of the criteria are set by companies that do oil changes. While the 3,000 mile myth is largely being eliminated, it’s still pretty often that you’ll get a handy little window sticker recommending you come back before you actually need to.
There are some drivers who will fall under the “severe” category, of course, so if you do any of the following you may want to work with that interval:
- Frequently driving off-road
- Repeated short trips under 32°F(0°C)
- Towing on a regular basis
- Mostly stop-and-go driving
Truth is, most people will fall under the category of normal when they’re driving, with a few exceptions for those who use their vehicles primarily in town for work.
Seriously, your owner’s manual is going to be your best bet to make sure that you’ve got the right mileage. Some of the newest cars on the market even have sensors reading the oil, which can make things much more accurate than guessing based on the mileage.
Older Cars and Synthetic Oils
When we’re talking about older vehicles, it’s important that we separate them into a couple of different categories.
For our purposes, we’ll refer to older vehicles as anything built after 1990 but before 2010, while we’ll use the term classic to refer to any vehicle which was built before 1990.
Older vehicles will undoubtedly benefit from the usage of synthetic oils, the increased “slipperiness” can reduce wear and tear on the motor and the extended lifespan can be of great benefit for vehicles which are under heavy use.
For the most part, if your engine was designed for usage with conventional oils you can usually double the “severe” usage interval. While it varies greatly depending on the vehicle in question, you can usually run about 7,500 miles without needing to make an oil change.
In classic cars, the recommendations become a little bit more complicated: there’s a lot of debate as to whether synthetics are useful at all.
Early synthetic oils contained a lot of esters. These compounds are quite hard on seals and gaskets, leading to issues with degradation of these essential parts in older motors. This isn’t the case anymore, but there are still some issues with using them in older engines which are still running with original parts.
There’s two issues here: the increased detergent load of synthetic oils and the fact that it’s “thinner.”
Quite often in classic motors there will be gaps in the seals and gaskets which are held together by the clumping and debris of conventional oils. The detergent load will wipe these from the motor quite quickly, and pre-existing problems can become much more apparent when you make the switch to a synthetic oil.
The lowered viscosity of synthetic oils also opens up a unique set of problems in classic engines where the oil leaks through any pre-existing gaps in the motor. Some classic motors are “looser” than modern engines and this can also cause leaking but this can usually be fixed by those who are handy about it.
Whether you think this is worth it in a classic engine is up to your own judgement. You can always switch back if it causes too many issues despite the persistent myth stating this is an impossibility.
Why So Much Longer?
If you’re unfamiliar with the processes behind synthetic oils, you might be surprised to know they can often last two or even three times as long as their conventional counterparts.
Synthetic oils are either Group III oils, which are extremely refined, or Group IV oils with Group V additives which are basically constructed from the ground up.
While many people think of oils as a single substance, they are in fact a complex mixture of waxes, hydrocarbons, and impurities. Group II oils, which most conventional motor oils are comprised of, have quite a bit of sulfur and nitrogen in them which shortens their lifespan.
They also lack some of the anti-oxidation additives which can be found in synthetic oils. These additives will keep the microscopic shavings of metal and other impurities which emerge as an engine is running from oxidizing and thickening the oil.
In fact, all oils can be recycled and re-used. With modern processes, this can often be done without any sort of loss of function although many places still end up sending “waste” oils off to be used as fuel oils.
The greater purity of synthetic oils is one of the main reasons why they last so much longer. Since there are virtually no impurities in a good synthetic oil, the potential for these damaging components to reduce the lubrication qualities of the oil simply isn’t there. Instead, the only damage to the oil will be from the accumulation of shavings, dirt, and other debris which come from the engine itself.
Many modern synthetic oils are also modified enough to reduce the damage which is caused by these contaminants through the use of detergents and anti-oxidizing agents.
Essentially, the oil is purer to begin with and treated to handle the impurities which come from the engine itself.
This leads to a greatly increased lifespan of the oil itself, and the greater lubricating qualities can also lead to reduced wear and tear on the engine itself.
Sounds like a good deal, overall, doesn’t it?
The real issue with using synthetics within cars is that they often cost quite a bit more than their conventional counterparts and that can be a big turn-off for the end consumer since it’s a much larger upfront cost.
On the other hand, in the right vehicle synthetic oils may actually save money in the long run if chosen carefully. The extended drain interval saves on the costs associated with changes and oil filters, and they’re also less volatile than conventional oils which means less topping off in between changes.
Just be aware that you may have problems emerge with older vehicles. The oil isn’t causing them, but instead as the motor gets cleaned they’ll emerge since the sludge left behind by conventional oils can hide problems.
Basically: synthetic oils are purposefully built for engines, instead of simply being refined from crude and having useful properties, which makes them the best for their purpose.
Conclusion
Knowing when to change synthetic oils in a vehicle without on-board monitoring that’s designed to run with conventional oil can be something of a pain. When in doubt consult your manual, and be careful to monitor your oil if you decide to make the switch.
Remember that you can always switch back later if you decide it isn’t for you, but the truth is that synthetic oils are the future and they really are the best way to go for the majority of engines. Give them a shot and you might be surprised.