Does Synthetic Oil Have Zinc In It [Fully Explained]

If you have a car with an older engine, you’d know that it requires engine oil with a high ZDDP content. If you want to use synthetic oil in such engines, it needs to have enough zinc. So, does synthetic oil have zinc in it?

The simple answer is most synthetic oils won’t have a good amount of zinc. But it largely depends on the exact oil brand and model you’re looking at. Different engine oils have different formulations.

does synthetic oil have zinc in it

So, you can also find synthetic oils that’ll have enough zinc for your older engine. Keep on reading to know why zinc was phased out and what type of oil you should use in older engines.

Does Synthetic Oil Have Zinc In It [Fully Explained]

Zinc was first used in engine oil in the 1940s. The compound used in engine oils is ZDDP or ZDTP. Because of its amazing antiwear properties, oilmakers kept increasing the zinc concentration in the motor oils.

Eventually, they took it too far and it was noticed that too much zinc started having a bad effect on engines. One of the major concerns was that using ZDDP reduced the efficiency of the catalytic converter.

catalytic converter

While zinc kept the engine from wearing out, this was a big issue. High zinc oils would also make the catalytic converters malfunction with time. So, the amount of zinc was reduced and kept on getting lower and lower with time.

Another reason why the concentration of zinc was so heavily decreased is due to the change in engines. The older engines had flat tappet camshafts. They were much more prone to wearing out and would require zinc.

But later on, engines with roller camshafts became popular. They didn’t need the zinc for protection. So, there was no longer any reason to use zinc in such engines given its reputation to damage the catalytic converters.

That brings us to the present day where most engine oils don’t have zinc. It doesn’t matter if you’re talking about conventional or synthetic oil. So, there’s a strong chance that a synthetic oil wouldn’t have a good amount of ZDDP if you were to pick one from the shelf.

With that said, it’s not impossible to find a synthetic high zinc motor oil for classic cars. For example, Valvoline VR1 Racing SAE 20W-50 Motor Oil and Royal Purple SAE 5W-30 Synthetic Motor Oil have high concentrations of zinc. You can check out my guide on top high-zinc oils if you want more options.

When it comes to classic cars with older engines, zinc is an absolute necessity. ZDDP is required for the break-in period as well as regular use. So, you’d have to pick a high-zinc synthetic oil if you can find it. Otherwise, you can use a zinc additive to the synthetic oil you’re using.

How Does Synthetic Oil Differ From Regular Motor Oil?

You need to understand whether you should use synthetic oil in older engines. But before getting into that, you should know about the main differences between synthetic and regular oil. That’s what I’ll talk about in this section. So, let’s look at the differences one by one.

01. Engine Protection

Simply put, the viscosity index is how the viscosity of the oil changes in relation to the temperature. If an oil has a low VI (Viscosity Index), it’ll change a lot with temperature. But if an oil has a high  VI, it’ll remain more stable during temperature fluctuations inside the engine.

oil viscosity

The molecules that make up regular motor oil usually have a lot of variance in their shapes and sizes. So, they have a lower VI and they don’t remain highly stable during temperature changes.

But synthetic oil has a much more uniform structure and that leads to a higher VI. Because of that, synthetic oil will flow better than normal oil at both hot and cold temperatures. So, it offers better protection against engine wear.

02. Volatility

You’d want the engine oil to stay in liquid form as much as possible. However, as the engine heats up, you can lose some of that oil as it evaporates. That’s not a good thing for engine oils.

So, there are tests in place to check out the volatility of different oils at higher temperatures. The smaller molecules of conventional oil are more prone to evaporate. So, only the heavier molecules will remain and that’ll reduce the cold flow of the oil.

But the molecules of synthetic oil are more uniform and the evaporation process will be slower for them. It won’t burn off as easily as conventional oil. Look for the ILSAC GF6 rating on the back of the oil bottle.

volatility certification

If you see that, it means the oil has passed the Noack volatility test. It means that the oil didn’t lose more than 15% of its mass during the test. So, synthetic oil is the better choice here without a doubt.

03. Level Of Deposits

Additives or viscosity modifiers are used in both regular and synthetic oils. But as synthetic oils have a higher viscosity index, you don’t need too many additives. Comparatively, you’d need to add more additives in regular oil to reach the same viscosity level.

The issue is that the additives are composed of much bigger molecules. So, the more you use them, the more deposits there will be. It’ll happen mostly in areas that have a high temperature.

For example, the piston rings are one of those areas. If you don’t change the engine oil frequently enough, the piston rings can get locked in place. At that stage, you’ll have blow-by and the cylinders are prone to getting damaged.

piston rings

But there will be fewer deposits when it comes to synthetic oil. Besides, there are more detergents and dispersants in synthetic oil. So, the engine will be cleaner overall.

In regular oil, you also have a higher chance of corrosion. That’s because of oxidation. But in synthetic oil, there’s less chance of that happening. So, synthetic oil will stay more stable and keep the engine from getting corroded.

Can You Use Synthetic Oil In Older Engines?

The short and sweet answer is YES, you absolutely can use synthetic oil in older engines. Even if you have a classic car, you’ll most likely find a synthetic oil for it.

The key thing to keep in mind is to follow the manufacturer’s guidelines. For example, Porsche approved using Mobil 1 Synthetic 5w50 and 15w50 oils in their classic cars. These cars have a larger engine and require a thicker oil.

Classic Car

Compared to classic cars, Porsche has factory-filled the newer cars since 1996 with 0w40 Mobil 1 synthetic oils. Since the 1970s, synthetic oils have been used in cars. So, you can use synthetic oil in older engines without any issues. 

There’s absolutely nothing wrong with using synthetic oil. But keep in mind that modern synthetic oils may not have enough zinc required for an old engine. So, you’d want to look into a synthetic oil with high ZDDP or add a zinc additive to the oil that you’re using.

Can You Add Zinc To Synthetic Oil?

As you’d know by now, older engines require zinc in the engine oils. Ideally, you should get an oil that has the ZDDP levels required for your engine. But if you aren’t finding a suitable option, the next thing you should look into is a zinc additive.

Lucas TB Zinc Additive is a great choice and you can add it to your synthetic oil. You don’t have to worry about adding zinc to synthetic oil any more than you would for your regular oil.

Just make sure you’re using the right viscosity oil and add the required ZDDP. You’ll protect your engine from wearing out by doing that and enjoy a much better performance from it.

Does Synthetic Oil Cause Leaks In Older Engines?

You may have heard that it’s not safe to use synthetic oil in older engines. And there’s good reason behind that. The cars used to leak due to the use of synthetic engine oils.

leaking engine oil

So, car enthusiasts decided to stay away from synthetic oil altogether. All of that is true. But those bad experiences many years ago don’t reflect how synthetic oils are made now. Back in the day, those synthetic oils were ester-based. They are organic compounds mixed with alcohol.

The seals were also made using ester. So, there was a compatibility issue. The ester of the oils would react to the seals and make them swollen. So, the seals would start to wear down and eventually cause leaks.

swollen seal

But since then, large strides have been made in making synthetic oil better. The base stock formulations that caused issues are no longer used today. So, you can’t let the bad experiences from the past determine the present condition of using synthetic oil.

There’s a lot of testing done in modern engine oils to test that they won’t damage the seals. Not just that, they go under many other tests to ensure quality. You can confirm it by looking at the numerous certifications on the back of the oil bottle.

According to Wayfarer, “Although in years past, it (synthetic oil) wasn’t recommended because of a lack of information and because of certain compounds that could damage older engines, those concerns have been put to rest. Today’s synthetics are perfectly safe for a twenty-year-old Ford or a fifty-year-old Benz.”

So, it’s not just me that’s saying that. And you’ll find that many people are using synthetic oil in older engines without it causing any leaks. All you have to do is get the right oil as per the manufacturer’s guidelines and you’ll be fine.

Another argument against using synthetic oil is that it has more detergents and it’ll remove the gunk inside the engine. So, it’ll expose the leaks and the engine will start leaking oil.

But that’s the wrong mindset when it comes to ensuring the long lifespan of an engine. Synthetic oil has more detergents and dispersants. So, they’ll do a better job at cleaning the engine. And that’s a good thing.

If you have sludge built up inside the engine, that’s the real issue. Not the fact that synthetic oil is cleaning it. In fact, sludges will block the oil drain holes and cause even more sludge.

If you have a bad seal, then you’ll have to replace it. But using sludge as a layer of protection for the seal will make your engine wear out a lot quicker. So, you should use synthetic oil to prevent this issue.

Should You Use A Thicker Engine Oil In Older Engines?

If you look at the oil cap of your engine, you’ll find the oil grade and viscosity recommended by your car manufacturer. For the most part, you should stick to that. The engineers who designed the engine know exactly what they’ve made and you should follow their guidelines.

However, engines aren’t meant to last forever and they’ll wear out with time. If you have an old car with many miles on it, you could have low oil pressure. The oil pressure light will indicate when you’re facing this issue.

The main reason behind this is that the clearance within the engine has increased with time. So, there’s more space and the oil is too thin to maintain pressure. So, using a thicker oil in that instance can increase the lifespan of your engine.

The important takeaway here is that you should only consider using a thicker oil if your engine has a lot of wear. Otherwise, you should stick to the original oil that your manufacturer recommended.

Think of the thicker oil as the last line of defense against a dying engine. It won’t make the engine better but it may survive a little longer. But if you have oil leaks, changing the thickness of the oil won’t solve the issue.


How is synthetic oil different from synthetic blend oil?

A mixture of synthetic and conventional base oils is used to create synthetic blends. So, synthetic blends are better than conventional oil but not as good as fully synthetic oils.

How do you know if your car needs synthetic or regular oil?

You can look at the manufacturer’s guidelines to see if your car needs synthetic oil. However, it’s perfectly fine to use synthetic oil even if your car only requires regular oil. But it doesn’t work the other way around.

Are conventional oils cheaper than synthetic oils?

Yes, synthetic oils almost cost twice as much as regular oils. That’s the main downside to them despite the added benefits. However using synthetic oil will also require less frequent oil changes.

Does synthetic oil protect critical turbocharger parts?

The temperature in a turbocharger can exceed 400°F and break down normal oil. But synthetic oil will offer greater protection as it won’t break down so easily. So, it’s the better choice for such high-performing engines.


Does synthetic oil have zinc in it? Now, you know that the majority of oils won’t have zinc because it has been slowly phased out. However, if you know what you’re looking for, you could find an oil with enough zinc. If you can’t find an engine oil with the right zinc concentration, you can use an additive instead.

Remember that too much zinc is just as harmful as not enough zinc. Keep those things in mind when you make your decision. I also have a ZDDP additive calculator guide that you’ll find useful if choose to use them.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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