Can Old Cars Use Synthetic Oil?

Taking care of your classic car can be a bittersweet experience. While it’s pleasant to have a classic beauty parked in your drive and run it around the neighborhood, you may have limited maintenance options as your car gets older. Can old cars use synthetic oil? This can be one of your questions.

Old cars can use synthetic oils without any issues. Synthetic oils benefit old and modern cars the same by offering higher protection against sludge and effectively lubricating engine parts. They contain additives that increase the engine’s longevity and require less frequent oil changes.

Read on to learn more about the benefits of synthetic oils and why there’s no harm in using them for your older car. I’ll also give you some tips about switching to synthetic oil. 

Table of Contents

• The Differences Between Synthetic and Regular oils
• Synthetic Oil in Older Cars
  • Harmful Components
  • Corrosive Additives
  • Lower Viscosity
  • Higher Costs
• When and How to Switch From Conventional to Synthetic Oil
• Can You Mix Synthetic and Regular Motor Oils?
• Final Thoughts

The Differences Between Synthetic and Regular oils

Regular engine oil is made from crude oil refined to some level that gives it enough viscosity to do basic lubricating jobs. It covers the engine’s vital parts to protect them against wear when they move at high speeds.

Synthetic oil also has the same crude oil base, while some brands like Pennzoil have natural gas as their base. But these oils contain additives that make them more effective in protecting engine parts. These additives may include anti-wear and anti-foam agents, dispersants, corrosion protectors, detergents, among others.

The biggest difference between synthetic oil and conventional oil is that synthetic oil is more refined while both are made of crude oil. As a result, synthetic oil has a more uniform molecular composition and is cleaner with much lower impurity levels. Plus, it’s the additives that make it more effective in lubricating and protecting the engine parts.

On the other hand, since conventional engine oils have irregular molecular compositions, they break down faster than their synthetic counterparts, requiring more frequent changes. Plus, regular oil can be more sensitive to extremely high or low temperatures, getting too liquid or too thick. As a result, it loses its lubricating abilities, potentially damaging the engine.

But regular oil has its advantages, which can be valid reasons why many car owners stick to regular oil.

The biggest benefit is that regular oil is more cost-effective than synthetic oils that cost even twice as much. Some cars don’t require synthetic oils, so the benefits can’t offset the added cost for car owners. These cars need regular oil and filter changes and general car maintenance to make sure they’re in perfect shape.

Synthetic Oil in Older Cars

Now, it’s obvious that synthetic oil can be more beneficial for your engine as it has a different composition from conventional oil and has additives that improve its efficiency. But can it benefit your classic car the same as modern cars?

Despite some prevalent ideas that favor conventional oil over synthetic oil for older cars, you can safely use synthetic oils for your old car. They’ve come a long way since their introduction in the 1970s, making many improvements to suit different kinds of cars.

But people commonly believe synthetic oil is bad for your old car because of past negative experiences. Here are the main reasons:

Harmful Components

Early synthetic oils contained a natural compound called ester, which could damage the soft engine seals and eventually cause leaks. While ester can be a good thing because it causes the seal to swell and increase compression, too much ester can lead to excessive swelling, making the seal soft and less tight.

Today, car oil manufacturers conduct different tests to ensure the oil is compatible with the engine seals. They must comply with a wide range of requirements to obtain certifications that ensure their safety. So, if the oil has trusted certifications, it’s safe to use in your old car’s engine.

Corrosive Additives

People think synthetic oils are bad for your car because they contain too much detergent or dispersant. These materials clean up gunk and sludge from your engine, which can cause engine leaks. That’s especially important with older engine seals as they’re not as tight as new ones and rely on deposits and gunk to create a tighter seal.

However, engine leaks aren’t the result of a clean engine. Instead, a faulty seal is the main culprit, which has nothing to do with gunk and sludge. In addition, a clean engine is something all drivers should be after because it increases the engine’s longevity.

You can tackle this issue by consulting your mechanic before switching to synthetic oil and asking them to examine the engine seals carefully. You may need to change the engine seals to new, tighter ones and reap the benefits of synthetic oils without damaging your seals.

Lower Viscosity

Modern synthetic oils are thinner than regular oils that are typically more viscous. Many people fear that if they switch to synthetic oils, they’ll raise the chances of leakage. That’s particularly a big concern with old cars with high mileage as their engine seals have become weaker.

However, not all synthetic oils are thin, and you can find high-viscosity ones if you look around. Plus, the lower viscosity means the oil’s more slippery, giving the engine parts better lubrication and minimum friction. Watching the oil levels constantly and regular oil changes can help prevent leakage.

With all that said, if you’re still unsure of what oil to use, consult your car’s manufacturer. They can give you a list of compatible oils for your engine and hopefully have tested them to make sure they’re safe. 

Higher Costs

Since synthetic motor oils contain chemically engineered components and additives that give them a uniform structure, they tend to be more expensive than regular oils.

Some people believe that the higher price of synthetic oils can be a logical reason to avoid them. That’s particularly the case for classic cars stored in garages most of the time. However, they don’t realize that investing in high-quality motor oil can be beneficial in the long run. That’s because they’re more effective, protect your car better, and need less frequent oil changes.

When and How to Switch From Conventional to Synthetic Oil

If you have a classic car that has always run on conventional motor oils, you may be concerned about switching to synthetic oil despite its proven benefits. As mentioned earlier, you can consult your mechanic and car manufacturer to make sure you’re using the right oil, and you’ll be fine.

There’s no right time to switch from regular oil to synthetic oil because it doesn’t have any rules. It’s just a matter of personal preference, and you can use synthetic oil anytime you want to. And even if you want to switch back to regular after using synthetic for a while, it’s OK.

However, if your car has high mileage (more than 75,000 miles) or you haven’t changed its oil regularly, the chances are high that it has lots of deposits and sludge in the engine. So, it’s better to do the conversion gradually to ease the engine into the process. This way, you can make sure the engine is becoming sludge-free without clogging anything.

Do oil changes in shorter intervals and change the filter every time you change the oil until the engine is completely clean.

Here’s a useful video about ideal oil change intervals for synthetic oils:

Can You Mix Synthetic and Regular Motor Oils?

With the higher prices of synthetic motor oils, some may mix their synthetic and regular oils to get a better bang for the buck. Technically, it’s possible to mix synthetic and regular oils because they have the same base (crude oil) but different purities.

Although mixing regular and synthetic oils doesn’t create compatibility issues, you can’t reap the full benefits of synthetic oils. You’ll dilute the oil’s beneficial components and mix it with impurities from the conventional oil. So, it’s not recommended unless you’re in a pinch and need to top off your synthetic oil with regular.

In fact, some commercially available synthetic oils are mixtures of conventional and synthetic oils. Known as synthetic blends, they come as opposed to fully synthetic oils that are purely synthetic mixed with additives.

Synthetic blends, also known as semi-refined oils, contain regular oils at lower concentrations but can give you the advantages of synthetic oils to some degree. They’re cheaper than fully synthetic oils, so you can use them if you don’t want to get an expensive oil.

However, mixing two types of synthetic oils isn’t recommended because they may contain different additives. Again, it may not damage your engine, but it can affect the oil’s efficiency and the engine’s performance.

Final Thoughts

Despite the myths formed around synthetic motor oils for older cars, there’s no harm in using them. When synthetic oils first hit the market, they caused some issues for older cars because of the ester content. However, modern technological advances make sure they’re compatible with all engine seals.

If you want to switch to synthetic oil, consult a qualified technician and your car’s manufacturer and check the oil’s labels to ensure it’s the best choice for your car.