Well my Glass Goose is still mothballed, although I oil and turn over its RX8 engine regularly.  One day I may get it finished (need to re-retire!).  Hopefully the engine will run one day.

My beautiful 2005 RX8 Shinka with 49K miles has gone from 1-2Qt oil
consumption between oil changes to 1 qt every 100-200 miles!   There are
no leaks nor smoking.  The engine still starts and runs fine. My oil changes, plug changes, coil changes, etc. have all been very conservative and the engine has never overheated nor been starved for oil.

The dealership thinks the engine is mortally wounded and wants to put in a new one for $6500.  They believe that the cat converter is handling the oil leaking past the seals (for now).

Although well out of the engine (time) warranty, Mazda will pick up 1/2 the cost of the engine replacement.

I'm not sure I have a lot of choice, but suggestions are appreciated.
$3200 is a lot to put into an 8 year old RX8.  I doubt I could get a more powerful, tuned engine for $3K instead of just replacing the engine with a factory-new motor.

I also wonder if I should run slightly heavier oil (maybe 10w-40) during hot Florida months instead of the 5w-20?

Scott Gettings

My RX8 has about the same millage and no problems.

Temporarily dis connect the cat and see if it smokes.

It may be the metering pump has failed.

Next test is take the metering pump off, block off the metering pump hole, and mix one ounce per gallon and see if the oil level in the pan decreases.

It is rare that the side seals on the rotor leak ever since Mazda went to a higher temp oil O ring. They may have gone back to a cheaper O-ring.

If the engine has good compression take it out and replace the rotor oil rings with teflon encapsulated silicone.

Good practice for your aircraft engine :) It comes apart in a half hour. If you organize the seals and  put them back where they came from you wont' need new seals.

One of the secrets is if you reuse the old oil scraper rings they must be spotlessly clean inside and out. Soak them in carb cleaner for a few days. If you use new scraper rings this will not be a problem of course.
The second thing to watch out for is don't nick the rotor wall between the two scraper rings when you remove them.
Very very important!!

These can be the same or just a little more than the stock oil O-rings from Mazda.

The proper 13B oil O-ring sizes are: The RX8 might be different.

0.093" section 4.68 inch ID
0.118" section 4.33 inch ID

I can vouch for the quality of the Creavey O-rings but some of those water TES o-rings from Mcmaster Carr I have seen are not as good. This is not to say they won't work. They just don't look as good around the joints as Creavey O-rings.

Viton is good only to 400 degrees F. The center of the rotor runs as high as 500 degrees F. I think 400 degrees F leaves's too little of a safety margin when 500 degrees F is available in TES O-rings at the same price probably.

http://www.rotaryeng.net/O-ring-size2.html

I just thought of something. The side exhaust port may be overheating the stock Viton oil o-rings in the rotors.


Paul Lamar

I agree with Paul here. Unusual to see oil rings fail. I would suspect metering oil pump also. Mazda dealers have been so blinded by replacing engines, that is the diagnosis any time a RX8 comes in,,,,it needs and engine. As bad as I hate to say it we no longer have technicians with abilities to diagnose anything anymore. If the computer doesn’t diagnose it, your out of luck. Then the diagnosis is "replace it"
Bob Mears


I checked with Mazdatrix on the melted side rotor O-ring idea. They have rebuilt and souped
up several RX8 engines so far. No sign of melted O-rings.

The leading contender for high oil consumption is the oil pan vent. There is some device in the large intake hose that is supposed to prevent this.

BTW Bob owns a Mazda dealership  so if you are near west Texas Mears Motors is a good
place to buy your RX8 and parts. Stop in and ask to see his 3 rotor powered scale
Spitfire.

Paul Lamar


Great comments thanks very much.  I asked my Mazda dealer "RX8 Expert
mechanic" (supposedly with 20 years experience) about the metering
pump, and he said that any significant defects would show up in the
computer error codes, and a significant failure should reduce, not
increase use.  I may try Paul's suggestion of removing it and looking
for any change in consumption.  (I assume it can't just be disabled
electrically?).

The mechanic did mention that significant oil loss should cause
dramatic smoking on startup, since the cat converter isn't hot enough
yet to toast the oil.   There is no smoking either on startup or when
running the engine hard.  Wierd!

Is it possible to easily open the oil pan vent apparatus to test the
theory that this may be defective?

One other issue:  this started right after an oil change, using my
normal Castrol GTX 5w-20.  I wonder if it is possible that the batch
of oil was bad -- such as too thin?  I could easily change the oil
again to test this possibility.

Removing and tearing down the engine myself isn't practical right
now.  I have not found any shops near central Florida that can offer
a rebuild so far.  My out of pocket costs will be about $3500-$4500
to replace, as Mazda will pick up $3200 even though it is out of
warranty.  Not an attractive option, for sure!

Scott Gettings

The are saying double and giving you the right price :)

I use Idemitsu rotary engine oil. If not that Mobile 1

Paul Lamar