Choosing the Best Oil Type for Your Mazda RX8

You simply cannot overlook the importance of choosing the right engine oil for any car, let alone a performance car.

Choosing the wrong oil can be extremely detrimental to the health of your engine. It can cause irreversible damage to the internal components, resulting in potentially expensive repairs.

The importance of choosing the right engine oil grows tenfold when it comes to unconventional motors like the Renesis engine.

Unlike piston engines, rotary engines are known to consume/burn oil by design. And if that sounds bizarre to you, chances are that you probably haven’t gone down the rotary maintenance rabbit hole yet.

If that’s the case, you might want to check out our RX8 buyer’s guide first.

But if you already know of quirks involved in owning a rotary-powered car and simply want to know which is the best engine oil for your RX8, then this guide is for you.

Read on as we discuss the best oil for your RX8. To make things easier, we’ve compiled a list of the options you can choose from.

Motor Oil Types

Whether to use mineral or fully synthetic oil is perhaps the most widely discussed concern among RX8 owners. Mazda recommends mineral oil for the RX8 but synthetic oil does make a lot of sense.

On one hand, using synthetic oil means better longevity and relatively cleaner combustion. But on the other, it strays from the manufacturer’s recommendation and costs more.

A Royal Purple engine oil container placed on top of Mazda's Renesis engine

We recommend going fully synthetic. It protects the engine, offering lower levels of friction and better longevity. Additives help clean the engine from deposits, and fewer impurities will ensure that it burns cleaner.

Oil Viscosity

The next doubt is oil viscosity. If you look at the owner’s manual, Mazda recommends using 5W-30 for RX8s in North America, and 5W-20 for cars outside of the North American market.

Generally, oil viscosity is to be chosen based on the climate in your region. So, if the environment you live in is pretty hot you’d want to go with a higher viscosity oil.

If you drive aggressively or attend multiple track days each month, then it’s better to use thicker oil.

However, this hasn’t stopped people from experimenting. Read around some forums and you’ll see some owners have tried mixing both types of oil and even different viscosities.

Sounds like a nightmare to us. We certainly don’t recommend you do that and advise you stick with a single oil grade only.

For the most part, RX8 owners have found synthetic 5W-30 oils to last longer than 5W-20 or equivalent mineral oils. That being said, 10W-40 is another common oil type worth considering if you live in a tropical region.

Few rotary experts suggest the use of semi-synthetic 10W-40 because it’s thicker and less likely to leave carbon deposits in the engine, preventing apex seal obstruction and stationary gear bearing failure as a result.

Levels & Change Intervals

Regardless of the oil grade you choose, the most important thing to remember is to check your engine’s oil levels regularly. Do this when your engine is warm and when you’ve let it sit for about 5 minutes after turning it off.

Mazda RX8 Engine Bay

It is recommended to change the oil and filter annually or every 12,000 miles, whichever comes first. However, the ideal recommendation is between 3,000 and 6,000 miles, topping up whenever necessary.

Best Oils for Your RX8

Whether 5W-30 or 10W-40, synthetic or mineral, no matter what you decide to choose, it’s important that you always buy from a well-known brand.

This includes reputable companies that have decades of experience in the business. Here are some of the best engine oils suitable for your Mazda RX8.

Valvoline High Mileage 5W-20

Manufacturer: Valvoline
Oil Weight: 5W-20
Type: Fully Synthetic
Available On: Amazon

Valvoline’s High Mileage 5W-20 oil comes highly recommended by RX8 owners. It is slightly thinner than the manufacturer-recommended 5W-30 but has proven to be extremely favorable for cold regions.

This oil contains additives and detergents to ensure that it remains free from sludge to keep the engine clean and protected. Because it is fully synthetic, storing it in hot or cold environments is never a concern.

Valvoline has also added detergents to the mix, ensuring that the oil remains free from sludge and other deposits. It is also certified by the American Petroleum Institute and has special seal conditioners to prevent oil leaks.

Valvoline High Mileage 5W-30

Manufacturer: Valvoline
Oil Weight: 5W-30
Type: Fully Synthetic
Buy on: Amazon

Valvoline’s High Mileage oil also comes in a 5W-30 variant. During cold starts, it will have the same low viscosity as the 5W-20 variant, but at normal operating temperature, it is slightly thicker.

This oil weight is ideal if you live in cold regions and if your driving style involves spending a lot of time at high rpm.

Other than that, you get Valvoline’s signature MaxLife technology that helps to keep your engine internals free of corrosion and rust.

If your car has clocked in over 75,000 miles, we recommend using this High Mileage oil to get more life out of your engine.

Castrol GTX MAGNATEC

Manufacturer: Castrol
Oil Weight: 5W-30 | 5W-20
Type: Fully Synthetic
Available On: Amazon

One of the most affordable oils for the RX8 is Castrol’s GTX with MAGNATEC. The IVA wear test proven oil offers excellent protection for critical engine components.

Additionally, this oil forms an extra layer of protection during warm-up to prevent the internals from wearing out. The oil is rated at 5W-30 but is also available in 5W-20, depending on your requirements.

Castrol Edge Advanced

Manufacturer: Castrol
Oil Weight: 5W-30 | 5W-20
Type: Fully Synthetic
Available On: Amazon

This is one of the best engine oils you can buy for your RX8. Engineered exclusively for high-revving engines, the Castrol Edge keeps metal-to-metal at an all-time low through the rev range.

The advanced synthetic blend offers maximum strength and performance. Castrol Edge Advance is a premium offering and can be purchased in 5W-30 and 5W-20 oil weights.

Pennzoil High Mileage

Manufacturer: Pennzoil
Oil Weight: 5W-30 | 5W-20 | 10W-30
Type: Fully Synthetic
Available On: Amazon

If you’re looking for the best high mileage oil, Pennzoil is the one to go for. Unlike other oil brands, Pennzoil uses its patented gas-to-liquid technology to convert natural gas to oil and does not rely on crude oil.

Pennzoil claims a low-burn off rate to protect the engine from power loss. The blend is specially designed for high-mileage cars with over 75,000 miles on the odometer.

Royal Purple High Performance

Manufacturer: Royal Purple
Oil Weight: 5W-30
Type: Fully Synthetic
Available On: Amazon

Royal Purple’s High Performance oil is specially formulated to deliver superior wear protection and increased fuel efficiency.

Designed with high-revving motors in mind, Royal Purple has engineered its range of 5W-30 and 10W-40 oils to offer better response and engine longevity.

Additional benefits include reduced wear, and enhanced protection against sludge and deposits, all while efficiently lubricating the internals at high engine speeds.

Mobil 1 Advanced

Manufacturer: Mobil 1
Oil Weight: 5W-30
Type: Fully Synthetic
Available On: Amazon

Mobil 1 Advanced’s 5W-30 oil protects critical engine parts by controlling oxidation to prevent oil breakdown, without negatively impacting oil viscosity.

The oil meets ILSAC GF-6 standards to help provide low-speed pre-ignition (LSPI) and timing chain wear protection alongside keeping the engine clean and improving fuel economy.

Overall, the Mobil 1 5W-30 is definitely among the best engine oil for the RX8.

Motul 8100 X-Clean EFE

Manufacturer: Motul
Oil Weight: 5W-30
Type: Fully Synthetic
Available On: Amazon

Motul has been in the business of making motor oils since 1989, and a lot of OEMs recommend using Motul, including Mazda. You really can’t go wrong with this label.

Their 5W-30 oil is designed to optimize fuel efficiency, reduce engine wear, and improve overall performance even when the engine is at its limit.

Extended drain intervals in among the many advertised benefits, but that won’t necessarily apply to rotary engines.

Best Oil for Mazda RX8: What’s Our Pick?

Silver RX8 at a car meet
Modifications like coilovers and aftermarket exhausts for your RX8 are always abundantly available.

Most of these brands offer oil in all the recommended viscosities. Be it 5W-20, 5W-30, or 10W-40, enough varieties are available to choose from.

Our top recommendation is 5W30 Castrol GTX Magnatec. However, this will depend on where you live, your driving style, and your use case. Mobil 1 Advance and Valvoline High Mileage are also highly regarded by RX8 owners.

Regardless of what you choose, don’t forget to stay on top of your maintenance routine. Rotaries don’t take kindly to neglect.

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