Castrol Edge Vs Royal Purple Oil [Which Is Better]

Picking the right engine oil for a vehicle is an extremely important decision for every car owner. An engine oil plays a key role in the long-term health of the engine. That’s why you must choose wisely. Two competitors in this space are  Castrol and Royal Purple. So, what should you choose?

That’s exactly what I’ll try to answer in this Castrol Edge vs Royal Purple guide. I’ll start by explaining the specifications of each of these oils and inform you which one to choose based on your requirements. So, let’s dive in!

Castrol Edge Vs Royal Purple Oil [Which Is Better]

I’ll talk about which oil will be the right choice for you in this Royal Purple oil vs Castrol Edge guide. But before delving into that, you must know a little bit of history about both these oils.

A proper understanding of each of these two oils will set the tone for understanding what’s similar and different in them. Then, you can compare which one will be better for your needs.

01. Introduction To Castrol Edge Oil

Castrol is one of the oldest oil manufacturers to be in business as they started in 1899. They have made different types of oil to fit the varying needs of users. But Castrol Edge is the finest oil that they’ve ever made.

castrol edge oil

It’s just not me that’s saying it. They claim it to be their strongest engine oil. And that’s good for a reason. First of all, it’s a fully synthetic oil that makes sure your engine is lubricated properly and protected at all times.

They also claim to use something called the Fluid Titanium Technology to improve the strength of the oil so that it takes longer to break it down. On top of that, it also lessens the friction between the different parts of an engine and gives a very good mileage. Some of the benefits promised by Castrol are:

  • 3 times stronger than the leading full synthetic oil.
  • 10 times better performance at high temperatures.
  • 6 times better protection against engine wear.
  • 10,000 miles between oil changes
  • Improvement in fuel economy (0W grades)

This oil is available in several viscosities including 0W16, 0W20, 5W20, 5W30, 5W50, 10W30, and 10W40. In terms of API rating, it is API SP/SN PLUS/SN certified. It also meets the ILSAC GF-6 requirements.

Along with the normal Castrol Edge oil, it’s available in different variants based on the needs of the user. Here are the three other models of Castrol Edge oil:

  • Castrol Edge High Mileage.
  • Castrol Edge Extended Performance.
  • Castrol Edge Euro.

Overall, Castrol oils are very good and they are loved very much by the users. I have seen many cases where people switched to Castrol Edge from a different brand and got much better results. Especially, in terms of slow depletion of oil and smooth engine performance.

It’s also a great pick for high performance engines. They are one of the top-performing brands in preventing thermal breakdown and viscosity breakdown at high temperatures.

02. Introduction To Royal Purple Oil

Royal Purple is a much more recent oil brand compared to Castrol as it was founded in 1986. However, that doesn’t mean that the Royal Purple oils are not good. They have gained a lot of fame in the oil market in a short period.

There’s no way this was possible if they didn’t provide enough value to their consumers. There are different Royal Purple oils based on their application. Let’s go through each of them quickly.

i) API Certified Oil

This is pretty much the entry-level oil variant made by Royal Purple. All Royal Purple oils are certified by API and they’re also full synthetic oils. If you use them, it won’t hurt the warranty of your car.

ii) HPS Oil

The Royal Purple High Performance Street oils are made for high performance engines that have been modified for more demanding use cases. It’s useful when the user wants to push the vehicle beyond normal performance and the engine needs a little bit more protection than the normal API oil.

royal purple hps oil

iii) XPR Oil

If you think of taking the Royal Purple HPS oil to the next level, then you’ll get the XPR oil. The Royal Purple Extreme Performance Rating oil is specially made for racing vehicles. It’s used in the racing engines of cars that participate in NASCAR, NHRA, and drag racing.

iv) HMX Motor Oil

This is the high-mileage oil made by Royal Purple. It’s ideal for use in vehicles that have already been driven for more than 75,000 miles. The oil is formulated to reduce the consumption of oil and improve the condition of hardened seals.

royal purple hmx oil

Are They Both Good Oil Brands?

Now, you know a little bit about the history of the two brands and the different types of oils we’re comparing in this guide. I strongly believe that both the companies in question make high-quality oils and you can’t go wrong with either of them. But why do I say that?

The most important factor in determining whether an oil is good or not is looking at its certifications. Whenever you’re getting an oil, it’s important to look at the labels of the oil.

In the front, there’s an API Starburst logo that represents it is certified by API and ILSAC. The specific use case of the oil is also mentioned there. For example, it clearly states whether the oil is supposed to be used in gasoline or diesel engines. If you’re confused about how it looks, here’s an example for you:

api starburst logo

That’s all you need to know about the API starburst sign. Apart from that, there’s also an API donut sign. It goes into further depth about the specifications of the oil to help the users decide whether it is the right one.

The viscosity of the oil is mentioned in the center and the API rating of the oil is mentioned. At the bottom of the donut, it also states whether the oil is known for conserving energy.

Those seals and certificates matter more than any boasting that the oil companies do. Because they’re tested independently on certain factors, when they meet the requirements, they’re given those certifications.

That’s exactly why I say both these oils are excellent brands. They’ve been around for a long time and they’re both reputable companies. When you grab any of these oils from your local stores, you’ll notice that they have these certifications. That makes both of them very reliable oil manufacturers.

Is Royal Purple Better Than Castrol Edge?

In terms of general specifications, the two types of oils don’t have a huge difference in them. However, Royal Purple is priced a bit more on the higher side compared to the Castrol Edge. That may make you think that it’s better than Castrol Edge.

But a heftier price doesn’t always mean a better product. Generally speaking, both oils are on par with each other. So, spending the extra bucks on Royal Purple isn’t worth it in my opinion.

With that said, Castrol also has nothing on Royal Purple in terms of the general specifications. So, I’d recommend using it simply because it’s priced lower and I don’t see any major difference between the two of them.

But now, let’s look into this matter with a bit more detail. The main thing that determines the right oil for you is the requirements of your engine. For example, if you want to use an oil that’s better in a racing engine, choose the oil that has a better ZDDP content.

Similarly, choose an oil that has a low cold cranking viscosity if you want a better performance during the winter. The main factor here is the requirements and which oil matches up the most to that.

Even in terms of price, I don’t think the difference between the two of them is a significant factor. The more important thing is to get the oil that matches the requirements of your car better.

If the specifications of both the oils seem to do a good enough job for your car, then it’s time for a bit of testing. You can run them on your engine one by one and see which one feels better.

Your personal experience will lead you to the right oil. A lot of people will prefer Castrol Edge and a lot of people will prefer Royal Purple depending on the engine. But either way, you’re getting a top-quality oil at the end of the day.

Hopefully, it’s clear to you what should be the basis for picking the right oil for you. But I’d advise that you should focus more on following the right practices if you want to get the most out of your car.

For example, changing the oil at the right intervals and replacing the oil filter when you do so is far more important than debating which of these brands is better. That’ll create a much better long-term positive effect on the engine.

Castrol Edge vs Royal Purple Zinc Content – Which Has More?

If you have an older car that has a flat tappet engine, you’d need an oil that has a good ZDDP content. Such engines need more protection and lubrication compared to modern engines with roller camshaft designs.

Let’s start by looking at Castrol Advanced. I was able to find the date sheet for the Castrol Edge Extended Performance Oil. The 5W30 variant of that oil contains nearly 730 PPM Zinc and 600 PPM Phosphorus.

Even though I haven’t come across a data sheet for the other variants of Castrol Edge oils, it’s safe to say that they’ll be in a similar range. So, the Castrol Edge oils aren’t that rich in Zinc.

If you want a Castrol oil that has a higher Zinc content, the Castrol GTX oils are much better at it. The classic Castrol GTX oil has about 1300 PPM Zinc and 1200 PPM Phosphorus. I’ve talked in detail about the Zinc content in Castrol GTX oils in that guide. Feel free to check it out.

Now, let’s get back to Royal Purple. As you already know by now, Royal Purple has many different types of oil. So, the amount of ZDDP present in them depends on the oil you’re choosing.

If you opt for the Royal Purple HPS oil, it has a very high level of ZDDP at nearly 1800 PPM Zinc and 1350 PPM Phosphorus. Compared to that, the normal API-certified Royal Purple oil has 850 PPM Zinc and 730 PPM Phosphorus in it.

The Royal Purple XPR oil has 1420 PPM Zinc and 1200 PPM. So, it depends on the oil you’re choosing. If you just want the oil, that has the highest ZDDP content out of all the options, you can just pick the Royal Purple HPS oil.

However, keep in mind that the additives in the oil are just as important to determine its performance. So, make sure you’re using the right oil for your car. I’ve compiled a list of Top 10 High Zinc Engine Oils that’ll help you choose the right oil for your car.


Do older cars require more Zinc?

Yes, classic cars incorporate a flat tappet camshaft design and they need an added layer of protection. That’s why oils that have a better ZDDP content is more suited for them.

Which oil is more expensive – Royal Purple or Castrol Edge?

Even though they are priced closely to one another, Royal Purple is a little more expensive. Royal Purple oil comes at nearly $9.78 per quart whereas Castrol Edge costs about $8 per quart.

Does synthetic oil damage older cars?

No, synthetic oils did damage older cars when they were first introduced. But that’s not the case anymore as synthetic oils have been upgraded to a great extent. They work perfectly fine now and offer great protection to the engine.

Why can’t I find Royal Purple in stores in my location?

There are some areas where Royal Purple is hard to find as they haven’t properly been distributed in all areas. In that case, you can select another option as most oils are close to each other in performance.


Engine oil is a tricky subject as each brand has many followers. In all honesty, many oil manufacturing are great and that’s why it’s so hard to choose which is better. I have shared my opinions in this Castrol Edge vs Royal Purple guide.

The truth is that both of them are reliable brands and you can’t go wrong with either of them. If you’re not sure whether to use synthetic or regular oil in your car, check out my synthetic vs regular vs semi-synthetic oil guide. Hopefully, you’ll find your answer there.

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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