That’s how my love affair with the rotary engine ended. It’s how the engine in my first car, the Mazda RX–8, ended.
Rotary engines are a gorgeous design of the internal combustion engine. Like a Spirograph, a rounded triangle sits in a two lobe peritrochoid housing with a shaft in the center that connects to the gearbox. As the rotor spins, it’s surfaces pull in an air/fuel mixture, move it to the side of the housing where it combusts, then the force of the combustion pushes the rotor around where the spent fuel is pushed out of the chamber. This cycle repeats at production speeds of 9,000 revolutions per minute, but can go much higher if tuned. The wonder of this design is that it works in a harmonic balance, unlike the piston engine that beats itself in a reciprocating motion. The nature of the rotary means a lot of power can be made with a light weight, compact engine.
It turns out that, for all the beauty in the design of the Renesis rotary engine, there was an unpredicted flaw.
Older rotary engines had notable flaws. Perfecting the material for an apex seal, the piece that sits at the tip of the rotor that seals the combustion chamber, was difficult. They typically became brittle and shattered. The Renesis finally had the right material. But that’s not the problem.
Two tangentially related issues culminated in ruin.
The first is that rotary engines, by design, must burn oil to lubricate the apex seals. Mazda did strenuous tests on the Renesis to prove reliability before the engine was released. Burning oil alone was not the problem with the Renesis, but it must have contributed.
The second issue is the mileage requirements for emissions systems, including catalytic converters, increased to 150,000 miles for the 2004 model year, the first model year of the RX–8, as part of EPA Tier 2 . The system was designed for a 80,000 miles, assuming there wasn’t another update between 1995 and 2004 that I’m missing. To improve the life of the catalytic converter, it is suspected that Mazda was forced to richen the air fuel mixture. For whatever reason, Mazda couldn’t or didn’t fully vet the changes.
As it turns out, two things that contribute to carbon build up are burning oil and running rich. That’s the flaw with the Renesis. Carbon builds up on the rotor housing and the apex seals, even in their perfected form, slowly wear down from grinding against the carbon deposits until compression is lost. The loss of compression, at least in my case, presented itself as stalling at idle.
Investigations were going on at least as early as 2007. That’s when my first engine was replaced at the behest of Mazda, for free, so they could inspect it for their research. It was right after my dad managed to flood it. I mistakenly thought that the flooding caused the carbon build up, which I thought was a ridiculous claim, so I doubted that my engine had actually been replaced. It turns out even Mazda didn’t have all the details and nobody was well informed about what was going on.
Frequent high revving can break up the carbon deposits, but the Renesis is ultimately a time bomb. Mazda released a revision to the Renesis in 2008 that added a coating, supposedly Teflon, to the housing to slow the build up, but it’s simply a stopgap. The harmonic balance is ruined by the scum that collects on the outside, and it wears away at the apex seals until the engine loses compression.
I found out that Medcenter Mazda quit buying RX–8s well before the production was canceled due to frequent replacements, and even kept surplus replacements because they knew they would use them.
A former rotary technician at Medcenter Mazda reckoned that Mazda canceled RX–8 production not due to emissions like most news outlets report, but because of the carbon build up problem. Whatever the case, he said they were all relieved when they heard production was canceled.
I was saddened when I heard production was canceled. I loved my RX–8. It was a driver’s car. Cradled in it’s cockpit, every control was perfectly situated for easy access. Just simple flicks of my little finger activated blinkers and windshield wipers. Thumbs could swap tracks and activate cruise control. The shifter was short throw and perfectly placed. I don’t even need to extol how brilliantly the RX–8 handles.
It was also fairly easy to maintain compared to other cars I’ve worked on. If you use an oil extractor, you don’t even need to jack up your car to change the oil. The filter, while difficult to reach, was up top. The radiator drain plug was perfectly fitted in a hole in the diffuser. The only thing I really hated about the RX–8 was that the headlights were impossible to change without taking the front clip off.
Other than the engine and the directly related components (i.e. the engine mounts are only good for 50,000 – 75,000 miles), the car was perfectly reliable. It’s not without warts; early on, there were plenty of reports of road debris busting oil coolers. My interior is starting to show its age with buttons cracking, springs breaking, leather wearing thin, etc. But I never had problems that were bad enough for me to give up on it until now.
I guess that is a lesson learned. I got my RX–8 in early 2004. It was as early as I could get it. I had been reading about its development and the development of the Renesis for years before. I thought the new engine had proven itself, but time tells a different tale. I’m left with the carcass.
I’ll always have fond memories of driving the Mulholland Highway across the crest of Santa Monica Mountains at midnight, and across the width and height of the United States; the joy I felt accelerating behind a marvel of engine design; riding around with my future wife before I could fathom where my life was heading; taking pride in my RX–8 at Sevenstock as the crowning achievement in rotary design. But it’s time to lay her to rest, along with my rotary obsession.