Signs your RX-8 Rotary Wankel Engine is Failing

The story continues

In Part 1 of this series, a brief overview of the RX-8 was provided, and the core issue—engine failure—was uncovered. That article was intentionally kept short and to the point. The rationale is simple: if you’ve found the article, you likely already know what the RX-8 is and are more interested in understanding the rest of the story. In today’s post, I intend to outline some of the common signs that your RX-8’s Wankel engine may be failing. These signs include:

  • Trouble starting when hot
  • Misfires, indicated by a flashing check engine light
  • Milky oil dipstick (spoiler, it might not actually be a problem!)
  • A drop in fuel economy
  • Rough idle when the engine is warm
  • A glowing emanating from under the car

Trouble Starting When Hot

While there are several issues associated with the RX-8 engine, the most common sign of trouble is extended cranking time when the engine is hot, sometimes even leading to a complete failure to start. This is a sure indicator that your engine is failing, and it’s probably the number-one issue people search for on the internet! If you’re interested in learning what causes this and what you can do about it, stay tuned for future posts.

Misfires, Indicated by a Flashing  Check Engine Light (CEL)

A quick note on check engine lights. It is a common misconception that a check engine will illuminate for any and all issues with a car. This is not the case (or at least it should not be). The check engine light is, in fact, a federal mandate from the EPA. Its primary purpose is to notify the driver of an emissions-related problem, urging them to address the problem as soon as possible.

When driving, if you notice a solid check engine light, it indicates a problem. Your vehicle may be emitting more pollutants than it should The official phrasing states, “your car may not be operating properly and could have a condition which wastes fuel, shortens engine life, or could lead to expensive repairs if left unaddressed. It could also be polluting the air.”

If on other hand, while driving, you observe a flashing or blinking check engine light, it signals: “a severe engine problem like a misfire is occurring which should be addressed quickly”. Why is a misfire particularly concerning? A misfire results in unburnt fuel passing through the engine and entering the exhaust system. That might not sound serious at first, but unburnt fuel reaching the catalytic convertor can cause permanent damage to it.

In essence, a blinking CEL indicates a catalyst-damaging condition that needs immediate attention. While it is technically possible to continue driving in this scenario, the longer you do so, the more damage you risk inflicting. Catalytic convertors are costly components, and damaging them is best avoided.

A compromised catalytic convertors does not just translate into a substantial replacement cost. They can lead to everything from a clogged exhaust system – increasing backpressure to hazardous levels –   to overheated catalysts that can glow visibly. Neither the engine nor its surrounding components are designed to tolerate  such extreme heat, paving the way for additional damage.

In summary, there are only two reasons you should ever see a check engine light: the issues mentioned above and during startup when it lights up to assure you it’s functional. 🙂

Milky Oil Dipstick

Observing a milky substance on your oil dipstick is not necessarily indicative of a problem, but it might suggest that your car is not reaching its full operating temperature. This phenomenon is most commonly observed during the winter due to the cooler temperatures and sometimes, higher humidity. The milky appearance results from a water/oil emulsion. Typically, the water originates from condensation forming in the vehicle’s sump.

Engaging in frequent short trips can exacerbate this issue, as the engine is not allowed to run at its normal operating temperature for long enough to evaporate or burn off the accumulated moisture. While in piston engines, such an issue could be a sign of a faulty head gasket, In the RX-8, it is relatively common. If the presence of it concerns you, consider taking your car on a longer drive to dissipate the moisture! Be warned, though: when it’s really cold outside, this might not fix the problem, as the RX-8’s cooling system is actually quite effective!”

A Drop in Fuel Economy

While the RX-8 is not exactly renowned for its  fuel economy (in the 3 years I ran a rotary I saw 14mpg to 22mpg with an average of 16.3 per tank), a noticeable decrease in your typical fuel mileage could indicate a decrease in engine compression, signaling the engine is on the bring of failure. The drop in efficiency arises because a lower compression means the engine is not functioning at its optimum level, thereby demanding more fuel per mile.

To better understand this, think of any engine as a pump – because, fundamentally that is what they are! If a pump’s seals aren’t sealing adequately, it will not be able to pump as much fluid with each stroke, the fluid will exit the pump at a decreased pressure. This diminished pressure illustrate the efficiency of the pump. In this analogy, the pressure correlates with the fuel economy you see (and in fluid dynamics gases are treated the same).

Rough Idle When Warm

Rotary engines,  especially the RX-8’s Renesis variant, are typically characterized by their buttery-smooth operation. This smoothness results from the fact that for every revolution of the engine, there are there combustion and compression cycles per rotor. This is unlike a four-stroke piston engine, which fires each piston every other revolution.

For a twin-rotor engine like the 13B, this equates to six firing events every complete revolution. However, it is important to note that the transmission input shaft on this engine, rotates at only 1/3 of this speed, thanks to the gearing relationship between the rotors and the eccentric shaft. In contrast, a four-piston engine would fire twice per revolution.

Consequently, if you observe any juddering or unevenness whilst idling, it is a definitive sign that something might be amiss, with ignition issues being a probable culprit.

Glowing Under the Car Post-Drive

Returning to the topic of catalytic convertors: if you notice a glow beneath your car after driving, particularly after intense or hard driving, it is a strong indication that your catalytic convertors overheating. This is serious concern and needs to requires immediate attention.


The points mentioned above are not an exhaustive list, but they are issues that I’ve experienced while running a rotary engine. I later discovered that many others have faced similar challenges. If you want to find out more, head over to to delve deep into the community and read about other people’s experiences.

In my next post, I intend to explore what I understand to be the underlying causes of rotary engine failure.

Thanks for reading!

Next Article: Why did the Mazda RX-8 Engine Start Failing?

Picture of the RX8 dashboard with warning lights illuminated.

This was from my 2004 RX-8, yes I have had two! The small orange/yellow icon of the engine below the red battery one is the Check Engine Light (CEL)

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