Should I Use Synthetic Oil In My High Mileage Car?

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Should I use synthetic oil in my high mileage car? You’ve probably been told not to use fully synthetic oils on your old vehicle or high mileage car, but do you wish to know the truth?

Well, the truth is simple!

What you were told is a “myth,” and most myths are not valid. There are lots of car myths you should take much seriously.

Regarding the use of synthetic oils in high mileage cars or older vehicles, we can assure you that synthetic oils pose no harm/damage to your engine, irrespective of whether the car is new, used, or old.

But if you own a high mileage, old vehicle, read on to understand better the type of oil you need for your engine.

Should I Use Synthetic Oil In My High Mileage Car?

Tips For Running Synthetic Oils On Older Vehicles

Firstly, it is important to say that synthetic oils are far better than conventional oil (from the onset). However, due to the additives and chemicals used in making synthetics, they are posed as “not good” for older vehicles and high mileage engines.

But, over time, manufacturers of synthetics have improved in their game, and right now, the synthetic oils you will find in the market are totally fit for all kinds of vehicles.

It is also important to say that both conventional oils and synthetics are from crude oil; the major difference is the processing stages/methods.

While conventional oils are passed through a simple refining process, synthetics are passed through sturdier processes and tend to include more additives.

The Myth

Regarding high mileage engines, the myth of synthetic oils not being good for such engines was gotten from this stereotype: a high mileage engine has been subjected to severe temperatures and pressure; thus, some of its seals and components may be weary.

Now, when synthetic oil is introduced to such an engine, there’s the possibility the oil will wash away those weary components and seals.

Basically, synthetics are refined with additives meant to wash the engine clean for better performance. However, some auto experts believe that such additives won’t work well with high mileage cars. But here’s the actual truth you should know.

The Truth

Synthetic oils won’t cause leaks or damage a high mileage engine. Using synthetics would even elongate the lifespan of your engine (if the car has been properly maintained all the while). However, if you’re switching from conventional oil to synthetic oil, ensure that you change the oil filter, too.

In fact, you should change the oil filter at intervals because a bad or clogged oil filter can lead to fatal, expensive damage.

More interestingly, using/switching to synthetic oils means that you’d have more time in-between oil changes. This is because synthetics last longer than conventional oils, and they are more efficient. There are two major types of synthetic oils, viz, fully synthetic oils and semi-synthetic oils.

Tips For Running Synthetic Oils On Older Vehicles

When the term “Older Vehicles” is used, it mostly refers to cars manufactured before 1990. Obviously, such cars aren’t as rigid and sturdy as the modern cars we drive these days.

Hence, there’s no doubt that running synthetic oils on such vehicles could lead to leaks. This is because synthetics will definitely clean out the grimes that may also serve as seals, thereby causing engine leaks.

It would be best to stick with conventional oils for such vehicles or get a special high mileage oil (recommended by the manufacturer or a pro auto mechanic).


As said earlier, synthetics are safe for all kinds of vehicles (including older cars that were well maintained). More so, there are some synthetic oils that are specifically meant for high mileage vehicles.

A very popular example of such synthetic oil is Castrol EDGE – this motor oil is meant for high mileage cars.

At this point, we hope that this article answers the question of whether you should use synthetic oil in your high mileage car. However, if for any reason, your mechanic insists that you shouldn’t use synthetics on your high mileage engine, ensure to stick with his recommendation (if you had always trusted his services).

Also, we would not recommend that you constantly switch between synthetics and conventional oils, or mix two oils of different viscosity. If you enjoyed reading this, kindly share it with other people.

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