The beloved Mazda Rx-7 with the 13B-REW engine was produced up until 1995 (and until 2002 in Japan). Nine years later, Mazda finally released the highly anticipated Rx-8 which continued in production until 2012. While the Rx-7 was touted for its tuning capabilities, the Rx-8 was unfortunately left in the dust from a performance perspective.
The Mazda Rx-8 uses the 13B Renesis, or 13B-MSP (multi-side-port), rotary engine. While it features the same 1.3L displacement as the 13B-REW it was naturally aspirated, lacking the twin-turbochargers featured in its predecessors. Producing 238hp and 159lb-ft. of torque, it undershot the FD Rx-7 engine by 42hp and 72lb-ft. compared to the highest output 13B REW.
In addition to the weaker power numbers, the Rx-8’s 13B engine also had a difficult to tune ECU. Combine that with the lack of forced induction and enthusiasts were not overly happy with the performance when compared to the predecessor 13B.
Despite its lackluster performance appeal, the lightweight nature and superior suspension and handling still made the Rx-8 a fun sports car to own. Winning international engine of the year in 2003, best sports car in 2004, and Car and Driver’s Ten Best list from 2004-2006, the Rx-8 was a great platform despite the power limitations. Additionally, it placed 3rd out of 7th in 2010 for the Best-Handling Cars Under $100,000, proving its worth as a fun-to-drive sports car.
Mazda Rx-8 13B Engine Problems
The Rx-8’s 13B Renesis engine is not praised for its reliability. The 13B engine suffered from a number of major problems that frequently left it needing a fresh rebuild prior to even hitting the 100,000 mile mark. Here are the top 5 common Rx-8 engine problems:
- Leaking Apex Seals
- Ignition Coil Failure
- Engine Flooding
- Catalytic Converter Failure
- Starter Failure
Other Noteworthy 13B Rx-8 Problems
- Excessive Oil consumption
- Clutch Master & Slave Cylinder Failure
1. 13B Leaking Apex Seals
Apex seals are the weakest link of the 13B RX-8 engine. The 13B rotary engine consists of two rotors which are shaped like rounded triangles. These rotors spin within a rotor housing that is oval shaped. The only parts of the rotors that come into contact with the housing is the 3 ends of the triangle. These are called the apex points and each point has an apex seal which is responsible for keeping compression within the combustion chamber.
The seals are use a spring which pushes them outwards against the rotor housing. Because the seals are metal and so is the housing, the seals are lubricated with oil to prevent internal damage.
Why Apex Seals Go Bad
There are a number of factors that can cause apex seals to fail. First, on a rotary engine, the intake air, combustion, and exhaust gases all take circulate within the same housing. This means the apex seals are constantly subject to changing temperatures. These changing temperatures can over time wear down on the seals causing them to crack.
Secondly, pre-ignition can create enough back-pressure against the seals to blast the seal out of the rotor and into the housing. When this happens the seal then eats up the rotor housing.
Additionally, as they are spring loaded, the spring force can weaken over time causing small compression leaks. And lastly, low engine oil can starve the apex seals of oil causing more friction between the rotors and housing, badly damaging them both.
Metal on metal tends to wear down eventually. When you have an engine that revs to 9,000rpms, the seals naturally wear down more frequently than they would on lower-revving engines. The 13B has two rotors in it which means there are 6 total apex seals, making this problem a lot more likely to take place.
Symptoms of 13B Apex Seal Failure
- Loss of compression
- Significant power losses
- Hard starts or no starts
- Engine stalling while running
- Constant misfires
When the seals begin to leak, or fail completely, the biggest thing that happens is the rotor housing loses compression. As compression is a huge part of combustion, the compression losses lead to significant performance decreases.
On the Rx-8 total seal failure is common. However, small leaks are almost guaranteed on any high mileage 13B. The seals are usually toast or leaking enough by the 100,000 mile mark to require a rebuild. If the seals pop out of the rotor and into the housing it will completely eat up the metal on the rotor and housing which usually leads to an engine replacement instead of a rebuild.
Apex Seal Replacement Options
Apex seals are usually what sends the 13B engine to the graveyard. There are two outcomes when the seal fails:
- Leaks: if the seals are simply leaking then you have the change to rebuild the engine or replace the seals. While this seems like the easiest option it requires pulling and completely breaking down the engine, making it an expensive and time consuming job.
- Seals pop out of rotor: if the seals end up in the housing, the rotor will drag the against the housing walls, chewing the metal up requiring new housings. While you can replace the housings and rotors to solve the problem the cost causes most people to just swap a fresh engine in it or send the car to the junkyard.
For those replacing their apex seals there are various aftermarket options that are supposedly more reliable.
2. RX-8 Ignition Coil Failure
Likely the least worrisome problem on the list, the Rx-8 is known to eat up ignition coils. The Rx-8 uses a coil-near-plug ignition system in which the ignition coils sit grouped together and are connected to the spark plugs via spark plug wires. The ignition coils are responsible for converting battery power into high voltage electrical currents so that the spark plugs have enough electricity to spark during combustion.
Ignition coils usually fire every other RPM on piston engines. On rotary engines they fire every RPM. When you factor in a 9,000rpm redline, the ignition coils are firing so much more frequently than they are on piston engines. Ignition coils are electrical components and therefore naturally wear down over time. As they wear down they lose their ability to convert the electrical currents into the voltage levels necessary for the spark plugs to fire.
Ignition coils on the Rx-8 usually fail every 30,000 miles. When you replace the ignition coils it is also recommended to replace the wires and the spark plugs. Fortunately, a set of OEM replacements isn’t too expensive nowadays and replacing these components is an easy DIY.
RX8 Bad Ignition Coil Symptoms
- Rough idling
- Hard starting
- Poor acceleration
- Check engine light
3. 13B RX-8 Engine Flooding
Driving your Rx8 through flood water is highly unadvised. However, engine flooding has nothing to do with outside water getting into the engine.
The RX8 is not an emissions friendly vehicle. Emissions are actually the reason it was no longer sold in the UK market after 2010. When an engine is warm it produces less emissions than when it is cold. So, a lot of manufacturers have different cold start cycles which are designed to warm the engine up as quickly as possible.
The cold start cycle on the 13B Rx-8 consists of the injectors dumping a lot of fuel into the combustion chamber while simultaneously feeding additional oxygen into the recirculating exhaust gases to further burn the exhaust gases and heat the catalytic converter up faster.
When an Rx8 is shut off too early in this cold start cycle, the engine can become flooded with gasoline. Essentially, there is a buildup of gasoline in the combustion chamber and there is too much gasoline for the spark plugs to be able to ignite the fuel and start the engine.
RX8 Flooding Symptoms
- Engine doesn’t start
- Smell of fuel while trying to start the engine
- Sound of engine trying to start but not igniting
Basically, your engine isn’t going to start. Flooding your engine can foul your spark plugs but it isn’t going to cause any serious harm.
How to Prevent 13B Engine Flooding
Flooding occurs when you shut the engine off too soon into its cold start cycle. Always warm your 13B rotary engine up before turning it off. By letting it warm up you can ensure that the excess fuel being poured into the combustion chamber is fully burned before the engine is turned off.
Never move your car from the garage to the driveway and shut it off immediately. Let the car run for a few minutes before you turn it off and rev the engine up to 3,000rpms a few times to burn the fuel. However, don’t rev the engine too high while it is cold.
How to Unflood an RX8 Engine
When you crank the 13B engine with the throttle wide open the fuel injectors get disabled. So, the process for unflooding the engine is to crank the engine while your foot is to the floor with the accelerator pedal. Obviously do this while the car is in park or neutral.
Crank the engine for up to 20 seconds while the accelerator pedal is fully pressed down. If it doesn’t start, then try cranking the engine for up to another 20 seconds without your foot on the accelerator. Repeat this process until the engine starts. If you have to repeat the process wait 5 minutes so that the starter has a chance to cool off before being punished again.
4. RX-8 Catalytic Converter Failure
Catalytic converters are the most important emissions system on most modern vehicles. The inside of a “cat”, as it is frequently called, is made of precious metals such as palladium and platinum. It has a honeycomb structure with these metals and essentially reduces harmful emissions through chemical reactions. The harmful exhaust gases have a chemical reaction with the metals inside the catalytic converter and breaks them down into less harmful substances like carbon dioxide.
Bad spark plugs, spark plug wires, and ignition coils are the most common causes of RX8 catalytic converter failure.
The catalytic converter can reach 500+ degree temperatures, making it very hot. When any of these three ignition components go bad, the spark plug doesn’t fire which leaves excess fuel in the combustion chamber. This excess fuel then gets passed into the exhaust system where it enters the catalytic converter and can then ignite, burning up the honeycomb structure inside the cat.
When this happens, the melted metals inside the cat clog up the exhaust system creating a ton of back-pressure in the exhaust system. With this much back pressure the engine struggles to produce power and rev. Therefore the most common sign of a bad cat on the Rx8 is struggles revving the engine past a certain level. Usually it will start not revving past say 8,000rpms and then it will quickly deteriorate until it no longer revs above 4,000.
Bad Catalytic Converter Symptoms – 13B Engine
- Engine gets stuck revving, won’t rev past certain levels
- Significant loss of power
- Check engine light and limp mode
Preventing and Replacing Failed Catalytic Converters
As mentioned above, bad plugs, wires, and coils is what causes cat failure. So to prevent this issue make sure you replace these components at first sign of them starting to go bad. Driving on a bad cat for too long can destroy the engine as it passes hot exhaust gases back into the combustion chamber.
If your cat has gone bad, you should start by replacing your ignition system and then replace the cat. Your first option is to replace it with an OEM cat, however, these are very expensive nowadays so this isn’t usually a recommended option. The second option is to buy an aftermarket catless or catted midpipe. This is a cheaper option and catless midpipes are cheaper than catted ones, but keep in mind they are illegal. The last option is the gut the cat by cutting all the metal out of the inside of it, essentially turning it into a catless midpipe, which is also illegal.
5. Mazda Rx8 Starter Failure
A starter is an electric motor that pulls electricity from the battery to crank the engine to get it started. Without the rotors moving combustion can’t take place. So, the starter is responsible for getting them moving so that the engine can fire up.
The starter in the RX-8 is extremely poor at starting the car in cold weather. The ignition system is also poor in colder weather which causes the already weak starter to have to crank longer to get the engine going.
Mazda simply used a bad starter motor for these engines. While there was an early recall in 2006 and the motors were changed thereafter, older vehicles are still prone to this problem, albeit less commonly than the 2004-2006 models. Bad starter, bad ignition system = failed starter motor.
Starter Motor Failure Symptoms
- Hard starts
- No starts
- Engine won’t crank at all
- Grinding noise during crank
- Starter engages but won’t crank
If you are hearing a clicking noise, it’s probably the battery and not the starter. If you do have a faulty starter the only option is to replace the starter.
Other RX8 Problems
The RX8 isn’t an easy car to maintain. Taking proper care of it is essential to longevity. While the major problems with the 13B engine are listed above, I wanted to call out a number of other issues or problems that these cars run into.
RX8 Oil Consumption
While oil consumption in a piston engine usually isn’t a good sign, it’s completely normal on the 13B. Because the apex seals need to be oiled, oil naturally burns off as the engine rotates.
If you have leaking apex seals you could see increased oil usage but it is not uncommon to need to add 1 quart of oil every 1,000-1,500 miles. You need to be absolutely aware of this as a rotary owner as low oil levels can cause apex seal failure. Keep a quart or two of oil in your trunk at all times.
Clutch Master & Slave Cylinder
For whatever reason, the clutch on manual RX8’s is problematic. The slave cylinder and master cylinder fail frequently. Over 5 years of ownership and 50,000 miles, these parts went out on me twice. The most noticeable sign is that the clutch is extremely soft or easy to push in. Getting the clutch to catch becomes a total pain which leads to grinding a lot of gears.
Manual Transmission Synchros
Manual transmissions have gear synchronizers which adjust the speed shaft so that the collar and gear synchronize their speeds before the engine reengages the transmission. The synchros notoriously fail on manual Rx8’s which will cause you to grind a lot of gears.
Synchro’s most frequently go bad from over shifting or pulling/pushing the shift knob too hard or far into gear. The best $75 investment you can make is buying a synchro saver which prevents you from putting the shifter too far into gear.
Always keep the oil levels high enough. Keep a quart in your trunk and top the oil off every 1,000-1,500 miles. Change the oil every 5,000 miles (at most) religiously. Don’t let the engine overheat and don’t let it get low on oil.
And my favorite: a redline a day keeps the mechanic away. Seriously, redlining these engines is good for them as it helps wipe away any carbon buildup.
Mazda RX-8 13B Renesis Reliability
Unfortunately, the 13B-MSP engine in the Rx-8 is extremely unreliable. However, most of the reliability issues are caused by poor maintenance and owners who do not understand the needs of rotary engines. With that being said, most of these engines will start to lose compression or completely lose compression by the 100,000 mile mark because of the apex seals.
Complete engine failure is not uncommon at the 80,000 mile mark either if the engine was poorly maintained. Even on a meticulously maintained 13B you are probably lucky to hit 125,000 miles before the engine needs a rebuild.
In addition to the likelihood of complete failure, the 13B rotary Rx8 also has a number of other failure points. While less expensive to fix, the starters, ignition coils, spark plugs and wires, clutch cylinders, and catalytic converters fail frequently. During my years of RX-8 ownership, I also ran into a handful of ancillary problems like broken door locks ($1,100 fix), waterlogged headlights, grinding synchros, sway bar end link failure, among other random problems.
The RX8 is a fun car to own and drive but in todays day and age I would not expect to find a reliable one that doesn’t have a fresh rebuild. All of this goes to show why these cars can be purchased for half the cost of an early 90’s Miata with double the mileage.
How has your experience with the RX8 been?