Is Synthetic Oil Bad For Old Engines?

So you have a car that is more than a few years old? Has it clocked 75,000 miles and is still counting? Then you must be wondering whether synthetic oil is the best choice for your car engine. We have researched this subject to help you decide what kind of oil is best for your older model car!

With improved technology in synthetic oil preparation, most cars can use synthetic oil regardless of their age or mileage. However, you should take precautions because synthetic oil contains esters, a compound that cleans off the sludge, which acts as a seal in older engines. With this sludge off, these older engines can start leaking, leading to engine damages in the long run.

In this article, you will learn all about synthetic oil and how it affects older engines. In the same vein, you will learn how to choose your engine oil and the best engine oil for your older car. Read on to find out more.

A mechanic pouring synthetic oil into an old engine, Is Synthetic Oil Bad For Old Engines?

Is Synthetic Oil Bad For Old Engines?

Before delving into synthetic oil details, here is the crucial question: what is synthetic oil? In simpler terms, synthetic oil is an artificially made oil using chemical compounds modified from petroleum compounds instead of whole crude oil.

Because of the chemicals and other additives, this type of oil is hard on seals in older vehicles’ engines. This will wear these down, leading to oil leakages.

Older engines have gaskets, seals, and other engine components that aren’t as tight as in newer engines.  Conventional oil builds up sludge in these components, which helps seal the gaps left by loose gaskets or seals. But because synthetic oils have high cleaning properties, they clean off this sludge, exposing the cracks and gaps that lead to oil leakages.

With oil leaking or burning more, you need constant oil monitoring, or else you risk damaging your engine. And this is all the more reason why you should know whether your car needs synthetic oil or not.

Can All Engines Use Synthetic Oil?

Typically, all engines can use synthetic oil. However, some manufacturers specifically recommend the use of synthetic oil for their engines. Some engines require synthetic blend or full synthetic oil. Always check your owner’s manual when choosing an oil for your vehicle, and when in doubt, take it to a professional for an oil change. Auto repair shops and oil change shops have equipment that tells them exactly what type of oil is recommended by the vehicle manufacturer for your specific engine. 

Is It OK to Mix Regular (Conventional) Oil With Synthetic?

Technically, yes, you can mix regular oil with synthetic oil since there’s no danger of doing so. However, synthetic oil performance is usually compromised since it’s highly refined and lacks the impurities found in the regular oil. By mixing the two, you lower the quality of synthetic oil, and you do not get all of the benefits of using synthetic oil.

How to Choose the Best Motor Oil for Your Car

Apart from price, full synthetic oil beats its regular counterpart when it comes to performance. It minimizes the hassles of frequent oil changes and the resultant sludge accumulation in the engine.

However, if the price is a deterrent, then you can select the blended one or rotate between the two while keeping track of the car mileage, date of the next oil change, and the oil type. Changing the oil type in your car has no adverse effect on your car engine.

However, it would be best if you always referred to the manufacturer’s manual to note your oil’s:

  • Viscosity grade
  • Oil specification

What to Consider Before Choosing the Best Oil for Older Cars

The Age of the Engine

Engines that have clocked 75,000 miles and above are considered high mileage engines. Also, if your car is older than seven years, it is deemed to be old. Here, you need to select the oil that has the best viscosity lest your engine will start stalling.

Temperature and Viscosity

You should go for oil that can tolerate high temperatures as well as maintaining its viscosity. With this ability, the oil will guarantee your engine protection and keep it in good condition regardless of the strain it’s exposed to.


You need to pay attention to the additives that explicitly explain the oil’s protective qualities for older engines. Many of these oils contain detergents, antioxidants, friction modifiers, and seal conditioners that help maintain a clean and efficient engine.

To be effective and avoid damaging your car engine, seek professional advice before changing the engine oil.

Which Oil Is the Best for Older Cars?

Mileage is not a concern for some people so that any engine oil can do so. You stand to increase performance, reduce wear, and increase the engine life by choosing the best engine oil for your car.

Castrol GTX Part-Synthetic High Mileage

This oil is found in common grades and protects your engine for your old engine car. To do this, it relies on its detergents that help avoid sludge deposits while the seal swellers minimize the amount of oil that gets into the combustion chambers.

Additionally, Castrol GTX High Mileage oil helps prevent emissions and catalytic converter system failure. Even with these functions, this oil is very cost-friendly.

Click here to see Castrol GTX High Mileage at Amazon.

Pennzoil High Mileage Conventional Motor Oil

This oil is an excellent solution for older engines that comes on a low budget and contained in an ergonomic bottle that makes it easier to handle. It has added properties that reduce engine wear and enhance protection for engines that have clocked 75,000 miles and more. Apart from preventing the formation of sludge and other harmful deposits, it’s the best option for preventing engine break down and failure.

Click here to see Pennzoil High Mileage Conventional Motor Oil at Amazon.

Valvoline MaxLife High Mileage Synthetic Blend

This semi-synthetic blend is designed for engines whose mileage has hit 75,000 miles and more. It has additives such as seal conditioners that prevent oil leaks, antioxidants that prevent oil breakdown, and friction modifiers that curb engine wear.

Click here to see Valvoline MaxLife High Mileage Synthetic Blend at Amazon.

Mobil1 High Mileage Engine Oil

This synthetic oil is known to protect even engines that have run up to 500,000 miles if regularly changed. Its high viscosity makes it high-temperature resistant, guaranteeing your engine protection at all times. Besides, it has seal conditioners and antioxidants that will do justice to the cracked and thinned seals in the engine.

Click here to see Mobil1 High Mileage Engine Oil at Amazon. 

Quaker State Advanced Durability Motor Oil

If you’re obsessed with keeping your classic or vintage car engine in good condition, then Quaker State's Advanced Durability Motor Oil is the best bet. It contains additives to neutralize combustion acids to protect your car's engine against corrosion. The Advanced Durability formula meets fuel economy standards for GF-5 industry standard motor oil.

Click here to see Quaker State Advanced Durability Motor Oil at Amazon. 

Royal Purple HMX Synthetic Oil

It is one of your engine’s best oils, even if it has clocked 75,000 miles and above. It’s a wonderful deterrent of sludge build-up and gives you peace of mind since you won’t be replacing it fast.

The icing on the cake is that this oil restores your engine performance, giving it a new lease on life while reducing oil consumption. While it comes at a cost, its benefits are worth the expense.

Click here to see Royal Purple HMX Synthetic Oil at Amazon.

Final Thoughts

In the beginning, there were issues with using synthetic oil in older cars. But technology has improved to an extent where synthetic oil isn’t as hard on older engines’ seals as previously was the case.

To learn more about the effects of synthetic oil, check out our post "Will Synthetic Oil Make My Car Last Longer?"

Share this article

Leave a Reply

Your email address will not be published. Required fields are marked *