Mildren Automotive


Is carbon killing your Rx8 engine?

The Rx8 Renesis engine has developed a pretty poor reputation for reliability and longevity in recent years, and quite deservedly so.  Owners and service agents alike need to be ‘up to speed’ understanding benefits of carbon reduction and removal and the real cost of no action.

Carbon is a normal bi-product of the combustion of petrol and air.  Your Rotary Engine is also designed to consume small amount of engine oil through Mazda’s unique oil metering pump (OMP) system, which initially helps lubricate internal compression seals before burning off leaving carbon behind.

In an ideal world, the carbon produced and left inside the engine should leave the engine with the rest of the exhaust gas, through the exhaust ports.  However the Renesis rotary engine seems to have trouble doing this, leaving deposits over everything.  It contaminates  the combustions first lines of defence – rotor faces, apex seals, side seals, oil control ‘O’ rings, corner seals and sparkplugs.



Left; The rear endplate, rotor housing and rotor have been removed.  As I removed the rotor, flakes of carbon not even bonded to the rotor fell off onto the centre endplate shown.  An engine with a history of running clean would not have flakes of carbon falling off like this. (courtesy Brett’s 03′ 4 port engine)



Right;  Intermediate endplate up closer showing flakes of carbon and an exhaust port partially clogged with carbon. (courtesy Brett’s 03′ 4 port engine)





Left;  Rotor removed heavily caked with carbon, some of the apex seals and side seals were jammed in.   Some of the oil control ‘o’rings on the side were jammed in so tight they broke upon removal. (courtesy Brett’s 03’ 4 port engine)



What is the effect of excessive carbon deposits?   Why does it make so much difference?

Excessive carbon deposits will cause any of the following;
1.  Engine oil contamination – reducing the useful life of engine oil
2.  Increases wear rates inside the engine – the seals, rotor housings & endplates wear at a significantly faster rate
3.  Seal functionality – seals dont move in their slots the way they should and jamming
4.  Engine compression loss – leads to poor air/fuel burning, poor starting, poor economy, poor performance, possible engine misfire.
5.  Once poor air/fuel burning has begun, the excessive production of carbon feedbacks on itself, creating a growing problem.

What are the symptoms of carbon buildup?
Unfortunately, for many, by the time any symptoms of excessive carbon emerge it is too late.  But for some, it may be a good time to look at some of the strategies for reducing the amount of carbon inside the engine.

Strategies for reducing carbon deposits inside your engine;
1.  Ensure your engine oil is clean and of good quality, so that oil metered into the rotor housing is cleanly burnt
2.  Ensure your ignition system is performing at its optimum – especially coils and plugs – for optimum combustion burning
3.  Driving style – dont drive the car like a ‘granny’, this car is like a greyhound – short trips, shifting gears at low rpm are to be minimised and driving under low load conditions to save petrol and money will cost you way more in the long run
4.   Quality petrol – good quality petrol will promote better and cleaner burning
5.  Regular removal of excess carbon buildups – I recommend at least once a year have your mechanic use Amsoil Powerfoam and perform an engine decarbonising process.


Amsoil Powerfoam is made to clean engines.  The fact that it’s designed to clean engines says something about it’s power. It’s not harsh on rubber, and can soak deep behind those Apex seals and springs, it’s the best product I know to use. According to Atkins Rotary, this is what Mazda uses to free seized engines. I’m not sure how accurate that is, but it is definitely a vote for powerfoam if I ever heard one!

Order your Amsoil Powerfoam from me today Make Enquiry, and I will send you a procedure to get optimum results from this product.