The rotary 13B-MSP (multi side port) engine is at the heart of the RX-8’s appeal and it spins to 9,000rpm, with a unique sound. It needs to be revved to get the best from it as it isn't like a conventional piston motor. Rather than the usual four-stroke cycle, the rotary engine has a triangular rotor that spins concentrically in an ovoid chamber. This design means the engine is very smooth in operation and also has only three major moving components. However, the rotor tips must be kept lubricated, which is where the engine’s reputation for using oil comes from.
The type of oil used in an RX-8’s engine is of vital importance. Ask any seller what type of oil they use. If they answer with anything other than 5W30 Dexylia mineral oil, then you might want to question them further on the engine’s health.
The right type of oil is crucial
It’s wise to ask for a compression test on any RX-8 you intend to buy. The engine’s rotor tips wear with use, which is why keeping it topped up with the correct oil is vital to its longevity. A compression test by a rotary engine specialist or Mazda dealer will show if the engine is worn; this will also show up as poor starting when the engine is warm. However, weak hot starting can also be due to worn or damaged coil packs. The Renesis engine has four coil packs, one for each spark plug, and they must be replaced every 30,000 miles. They cost £80 each to replace, so it’s worth finding out when they were last changed. Spark plugs and leads are also sensitive to wear, so again check when they were replaced. It’s best to use NGK or Magnecor HT leads as replacements for the originals.
Worn or damaged coil packs will be noticeable thanks to a loss of power, but any lack of power could also be down to failure of a secondary shutter valve in the inlet manifold. This valve provides air to the secondary injection system, and a broken valve will be heard as a ticking noise in the engine bay.
If cold starting, you should always try to avoid switching off the engine until it is completely warmed through. The ignition system pours a lot of fuel into the rotary engine to warm it and the catalytic converter as quickly as possible, so turning off the motor when cold will flood it and restarting can be a problem. This also causes fuel to be dumped into the catalytic converter, which results in hot spots and shortens its life, resulting in a costly replacement. An original Mazda item will set you back around £1,400, which is why many owners opt for an aftermarket catalytic converter from around £200, or a de-cat pipe. It’s also worth bearing in mind RX-8s have high carbon dioxide emissions, so a post-March 2006 car will be expensive to tax.
Torque is on the low side in both models
Using a rotary design also means a small capacity of 1,308cc, so it’s no surprise the engine needs plenty of revs to get the most from it. It also means the Renesis engine does not offer as much torque as its rivals with similar power generated by much larger capacity engines. The 192hp engine actually offers more torque than the 231hp motor, generating 162lb ft and 156lb ft respectively.
Countering this, the 231hp model comes with a six-speed manual gearbox as standard where the 192hp makes do with a five-speeder. If any RX-8 you look at has an automatic gearbox, it’s an import as Mazda did not offer the auto in the UK. Both manual gearboxes are tough and reliable,and should have a crisp, easy change. Clutches on early cars could be prone to early wear and failure, but Mazda replaced most under warranty. Even so, an RX-8 clutch may need replacing every 30,000 miles. Mazda revised the final-drive ratio for the 2009 model year car, shortening it from 4.444:1 to 4.777:1 for better initial acceleration and in-gear performance.
There is a heat shield on manual transmission cars called the Dynamic Damper Heat Insulator that can crack or fall off. This was subject to a recall by Mazda for faulty items to be replaced with a modified version, so there should be no rattles from the transmission if the recall has been carried out. A carbon fibre propshaft not only saves weight in the RX-8, but also helps reduce transmission losses to compensate for the engine's lack of torque.
Take a look underneath the car for any signs of damage or corrosion on the sump. The final area to check with an RX-8 is the oil cooler and air conditioning radiators in the front bumper as they can rust. Some owners fit mesh grilles to prevent these radiators being hit by stones, which is a good sign of a caring owner. Some RX-8s may have had their front oil pipes replaced due to rust caused by water ingress from the front wheelarch liners. Mazda fitted new oil pipes and arch liners to cure this.
Owner's view
"The RX-8 is a car that requires buyers to go into ownership with both eyes wide open. It pays to do your research and if you buy a car with a good engine you will enjoy many miles of excellent driving fun! Forget about the poor mileage the car gets on an average journey, forget about the high road tax costs, just enjoy the performance and noise it makes at 9,000rpm - it is addictive."
Danny Zaat