anyone who experiences engine knock (sounds like marbles hitting sheet metal) upon acceleration, call 949 222 2638. this is Mazda's consumer compliance line. Voice your concerns, otherwise this problem will never be remedied!

 

I like how one person has a problem with a car, and immediately assumes it's a widespread defect.

 

Hey there have been enough posts on the board about this to warrent this particular post, myself included.

I know of several, including one from England, and it's on both Auto and Stick.

The real trick is getting it to reoccur for the Mazda techs, and thats a whole different ballgame.

 

Back to reality guys... in case you don't know... this marbles in can rattling you talk about has been around for some DECADES with all rotaries to the best of my knowledge.

MY RX-2 did it many moons ago and my RX-8 does it today, and it has NEVER hurt anything, or changed my love of the rotary in any way.

All your spouses and/or girl/guyfriends don't sound the same, why should all cars sound the same. After all you are taking your 'piston' knowledge and trying to apply it to a 'non-piston' engine. You need to accept new realities, i.e. the rotary reality... and it is not the 'piston' reality.

Forget it and drive!

PS there are many newbie threads about this noise, and the answer is mercifully the same... forget it and enjoy the ride and the new noises!!! :D

 

I was not surprised when I heard my engine knock using 87 octane. I would be concerned if my engine knocked using 91 octane.

 

Is this your first rotary engine? I'll bet $50 it is....

THE SKY IS FALLING THE SKY IS FALLING!!11!! OMG!!

 

Do you want me to PM you my address so you can send me the $50.

 

It's hard to say without actually hearing the noise.

I know if I heard appreciable knock from *any* of my rotaries I would be seriously concerned. Knock/detonation is definately not good for a rotary and it's not normal.

The above, however, assumes that what the writer is describing is actualy detonation - which is impossible to know without actually hearing it first hand.

The '8 does have a raspier exhaust note than my FC or FD and I could imagine how someone might mistake the sound for knock. BUT - if I actually did experience detonation in the '8 I would most definately be very concerned.

 

hmmm...seeing all these threads maybe we should get some of our senior fellows with old RX-7s(and prior!) to get a sticky or something to act as a Rotary engine Primer for all of us first time rotorheads.

Something very simple as in noises, sounds, common strengths and weaknesses. This way we can point them to a common article. I have learned a lot about newtorking and stuff like that through other tech forums that have had primers.

just a thought for some of our more ambitious owners!

 

The reason I was not suprised to hear knock from the 8 is because others have said they heard it. I stopped using 87 octane because I was concerned .I am 98% sure the sound I heard is knock. The Knock is very loud and can be heard over the raspy exhaust note. I heard it a few times on separate fills but ONLY when using 87 octane.

 

One of the reasons I stick with 91 octane is that I don't want to push the envelope and have detonation due to insufficient gas octane. The description of marbles being dropped into a tin or popcorn sounding are fairly accurate ones.

One thing though - if you continue to experience knock, you will damage the engine - so it might be wise to change to 89 if you're steadfast against going with 91 as recommended in the manual.

 

I've heard it using 87 octane also. I've since then use 89 and I hear it once in awhile when I'm on full throttle. I cant say I've heard it using 91 because I dont use 91.

 

That's enough for me to think that using less than 91 is just asking for disaster. Perhaps if you're never hard on the gas you might get away with it, but for me that's just not how I drive.

IMO the money saved by using 87 or 89 just doesn't justify the possibility of damaging the engine.

 

Are you implying that using anything lower than 91 octane will damage the engine? The manual states you can use 87 and higher. What is your claim based on?

 

My claim is that continued knock will damage your engine.

Others have stated that when using 87 or 89 they have experienced knock.

I'm not saying that you will damage your engine by using 87 or 89 - however, in my opinion, by doing so you are increasing your risk of engine damage based on people reporting that they have experienced knock using 87 and 89 octane.

Just my opinion - feel free to take it with however much weight you wish.

 

Also remember that the effective octane is lower in places that use oxygenates, especially in the winter.

That said, I don't see why anyone would use less than 91.
I use 93, 94 when it is convenient.
The difference between a tankfull of 87 and a tankfull of 93 in the DC area is about $1.
That is $500 for every 100,00 miles.
Go find an insurance policy with those kind of terms.

 

FYI - I ONLY use Shell Super Unleaded Premium (93), and always have, BUT the detonation (pinging) has begun on my car!

They replaced my "standard" spark plugs with the hotter plugs last time it was in the shop being looked over. Now, when the car is cold or first driven, it's fine. As soon as it warms up, though, it begins.

Anything over half throttle between 3000 and 4500 rpm will cause detonation (in ANY gear) that can be heard over the radio being on! It was warm in Houston over the weekend (80 degrees), so I had the air conditioner on ferrying the boy to basketball practice, and the car was detonating almost constantly during any type of acceleration.

I ordered the "standard" plugs, picked them up yesterday ($80 just for the two), and am going to install them tonight. I'll report back on the results, but if any of these "complaints" are after the install of these plugs (and you live in a warmer climate), it might have nothing to do with octane.....

 

hi dunno,
I use Shell 87 and have never heard this on my car. Do you hear it during light acceleration, say from when you're accelerating from a traffic light during heavy traffic, or is this hard acceleration as in racing?

thanks,
rx8cited

 

i have an auto 8 and use only 93 oct. and still hear this engine knock. took it to Mazda service and they say it is "detonation" and is normal. however, for a new vehicle this is hard to accept since the noise is even louder than the engine itself. i will call that number.

 

I use 87 exclusively and never get knocking. Please don't generalize from your experience and expect it applies to all of us. I am quite happy with my driving experience. If and when I ever hear knocking I will increase the octane level of my gas. Until then, 87 it is.

 

I'm not going to be convinced that it is indeed "knock" until someone actually proves it. Show me the output from the engines knock sensor at those throttle positions.. Show me EGT increases. Show me something other than "I hear a funny noise in my engine."

Until I see that, or my engine itself expires while making said noise, I remain unconcerned.

 

My 2¢ -

My RX-8 has been making a pinging, detonation-type noise for quite a while.
It is more pronounced in some RPM ranges than others and at different load levels.
Having heard that type of sound many times on various vehicles, I was concerned that it is pre-ignition so I investigated it more carefully:

1) The spark plugs show no indication of detonation.
2) My compression remains the same, showing no indication of engine damage.
3) A datalog of the knock sensor shows no activity.
4) The noise is clearly coming from the right side of the engine.

The last point is significant because the spark plugs are on the left side of the engine. Combustion chamber noises would have to be on the plug side.
The exhaust manifold is on the right side, however.

I suspect that there is some kind of post-exhaust combustion going on in the exhaust manifold making this noise.

Also important to note -
The manual tranny makes a terrible racket. It grinds and whines and rattles. This is true in all of the RX-8s I have driven.
It can be heard clearly under acceleration at all times.
At some point I will try some Redline MTL or MT-90 to see if it quiets that component of the unpleasant noise. This adds to the noise at all the right (wrong?) times making it sound more "centered" in the engine bay, so a careful listen from the passenger seat is necessary to really hear where this "detonation" noise is coming from.

 

As I reiterated in a later post - I don't expect anyone to do anything based on my opinion - I can generalize if I want, it's up to the reader to feel compelled that it applies to them or not. Everyone, please feel free to place as much or as little weight in my generalizations as you see fit. If you want to use 87 - excellent - but I'm not going to because I deem it a risk.

The good thing about free will and such is that we can all do whatever we want.

 

For those using 93 and higher: Mazda recommends 91 "for optimum performance" as they say in the owners manual. Using higher octane than recommended offers zero benefits. Oil companies, auto manufacturers, and petrochemical engineers all say this. Check their websites. Using lower than recommended, I understand there is a debate, but using higher is a waste. You will get no greater performance, no less knocking, no cleaner engine, no nuthing. It's your car and your money and obviously you can do what you want; just be aware you have succumbed to hype and you are the one they saw coming a mile away.

Also for the record, CA or at least San Diego, does not offer octane greater than 91. At least I've never seen it; perhaps some specialty shops might offer it. From some of your posts it seems like higher octane levels are more widely available in other states.

 

True, and I'd add the the potential to loose power is there since higher octane means a slower flame front and harder light-off.

However, since there is the idea that pre-ignition is possible on this motor in stock form and that oxygenated fuel will often have an actual octane that is lower than the rated octane, it is not a bad idea to use 93 since it is only marginally more expensive than 91.
Add to that the fact that I am running even more advanced timing and leaner mixtures and 93 is a logical choice.

The "premium" fuel from most refining companies also has the more expensive detergent package, but that is of little concern in a properly tuned motor, especially one without a valve train.