Raevik

So I took my car in for some minor repairs.

While there, I was told some interesting tidbits that all the service reps all agreed on (they were interested in the conversation and piped in).

1) Never put anything OVER 87 in the car, especially in urban driving. It will cause a carbon/residue buildup that can foul plugs. When I asked why it was printed in the owner's manual to use premium, he hesitated a moment, then said "Yes, well, they also tell you to change your oil at 7500 miles. They are trying to generate money by offering you the minimum service required to keep the car going while potentially causing problems to generate revenue. You have to use some common sense and change the oil out at 1/2 that in urban driving"

2) You have to DRIVE this car. All the rotaries are this way. "We've had 2nd and 3rd generation RX7s come in here driven by lawyers who drive like grannies, and they had full engine replacements at 20,000 miles because of 'frozen' apex seals". The car NEEDS it. It must be driven at high rpms. If you don't do it, it will break down.

3) It's impossible to "knock" the Renesis with low gas octane because there's no valves to ping. (I'm wondering what's controlling fuel intake and exhaust...I thought there were valves at every port going into and out of combustion, but what do I know) There's no reason to ever use more than 87 because of this reason as well as reason number 1.

I'm not sure if what they were saying was true, but it's definitely not the "party line" I've been seeing/reading/hearing. I found it interesting he even went so far as to accuse the writers of the manual of being deceptive and trying to do only the minimum.

Are these items BS, or what?

-8-

I don't think a rotary can knock because of lack of pistons. Some have said there is only a slight compromise of power when using regular over premium gas.

And I guess I am OK with your #2 point, since I practically bring it to 9k RPMs every shift.

HeelnToe

It sounds like THEY are the ones trying to generate revenue

As far as I know, knock has nada to do with valves. Knock occurs when the fuel explodes prematurely due to heat/compression, instead of waiting for the spark. Low octane fuel goes boom at lower compression/heat levels, good fuel resists going boom under high heat/compression until it's actually sparked by the plugs.

The "ping" you hear is, I believe, that premature detonation.

Ajax

Well, I don't know about gas over 87 fouling the spark plugs. I do know that 87 burns quicker and more efficiently in a rotary and is perfectly acceptable to use in the renesis engine, however, low end gasoline generally doesnt have the detergents that clean fuel injectors like high grade gas. I personally run 2 tanks of 87 then 2 of 93 just to keep them clean. Furthermore, chevron's techron probably does nothing for the renesis as it's supposed to remove carbon deposits from the valves (in turn pushing them into the engine) but we don't have valves so what's the point?

I'm about to hit 5000 miles and when I do, I'll be getting my oil changed.

I've never heard of frozen apex seals. Any car that you want to keep the engine running well has to be driven at least once in a while. In order to keep the injectors clear, you need to rev it high at least once in a while. I'll ask Don about frozen seals the next time I see him.

This is not true. The renesis, just like any rotary can ping if the apex seals collide with the housing. Generally speaking, if that happens, you're going to have issues. Gasoline is not going to cause it to ping, but running too low of an air/fuel mixture or too high of a boost might. With the stock settings, it probably is impossible to ping the renesis.

RobDickinson

We have a winnah!

Sure knocking - or detonation , can happen in a rotary, and its a killer. No need for valves etc.

Its just the fuel/air mix going pop before it should due to engine./air temp.

The 8 has a knock sensor which protects the engine prety well - but higher cotane fuel will help stop detonation.

Raevik

Right.

Premature detonation of the AF mix due to high compression/temps causes the ping/knock (same thing?). I was confused though, when he mentioned valves, because I've also heard mechanics mention valves pinging, so I thought he might be speaking in half-truths.

I've never actually had someone warn me away from premium before. I've seen/heard people say that 87 might be fine since it's cheaper and more efficient since it burns with a hotter flame front, but I've never heard of premium gas causing carbon buildup. They were saying basically that you wouldn't burn it all off and that's why it would cause reside and potentially harm the plugs, etc.

HeelnToe

How do you know that? Not trying to be a jerk, I just don't know much about rotaries beyond basic theory... trying to learn

From what I know, fuel is fuel once it's ignited. Octane simply measures how difficult it is to ignite it. Or, better said, how resistant it is to premature ignition.

Quote:

This is not true. The renesis, just like any rotary can ping if the apex seals collide with the housing. Generally speaking, if that happens, you're going to have issues. Gasoline is not going to cause it to ping

I always thought "pinging" was the gasoline igniting prematurely, and in the case of piston engines, at the worst possible time: when the piston was still early in it's travel upwards. I'd imagine a rotor has a similar compression phase? I'd imagine if low octane fuel went BOOM before the spark, it'd resist the rotor's compression phase, and make a PING?

Ajax

87 burns more efficiently in a rotary because less of it is wasted. Octane is exactly what you stated, resistance to ignition. The problem with a rotary is that gasoline that is not burned is swept into the exhaust chamber.

Detonation is premature ignition.
Pinging is the actual impaction of metal on metal. <-- no.. i may be wrong...


"Knocking (also called pinking or pinging) in internal combustion engines occurs when fuel in the cylinder is ignited by the firing of the spark plug but burns too quickly, combusting completely before the optimum moment during the compression phase of the four-stroke cycle. The resulting shockwave collides with the rising piston, creating a characteristic metallic "pinging" sound. The fuel is normally ignited slightly before the point of maximum compression to allow a small time for the flame front of the burning fuel to expand throughout the mixture, so that maximum pressure occurs at the point of maximum compression. It is only when this flame front arrives too early, for whatever reason, that the knocking effect occurs. If allowed to persist, knocking can cause vibration and damage to engine parts."

HeelnToe

Ah, OK... interesting... what would the metal-on-metal "ping" be in a piston engine?

Ajax

Like i said. Reread my post. I'm just flat wrong.

Meowloud

The higher the octane, the higher the 'flashpoint'. Energy produced can also be greater.
A higer octane gas, if not fully spent, can actually hurt your mileage by being disposed of in liquid form out of the exhaust.

A lower octane has a lower flashpoint, and burns more completely... but may flash too soon, causing inefficiencies.

Basically, try all and see which one 'feels' better to your car.

Ajax

Furthermore:

"Knocking is a different phenomenon from pre-ignition, which occurs when the air-fuel mixture in the cylinder ignites before the spark plug fires. Pre-ignition is caused by heat buildup in engine components or overheating of the air-fuel mixture during compression, and cannot be prevented by delaying spark plug firing. As such, if pre-ignition is allowed to continue for any length of time, severe engine damage can result."

HeelnToe

LOL, well, not necessarily... if you DO get detonation, it's gonna try and push the rotor in directions god never intended, lol...




Alright, I'm still playin' devil's advocate on this one... why would lower octane burn more efficiently in a rotary? The fuel doesn't know it's in a rotary, it just knows someone just squeezed the heck outa it and ran a kajillion volts through it.

I always thought that once sparked, a flame was a flame...? I get that it's easier to ignite, but are there any articles/research sugggesting that it burns more thoroughly as well?

GiN

Knock, ping, premature detonation, same thing. Chances of this happening are higher when using low octane gasoline.

Cheap gas, not necessarily low octane gas, increases the chances of plug fouling.

Frozen apex seals occurs when all the lubricants on the moving parts of the motor have left the area, causing the internal metal surfaces to be bound together. Running the motor frequently at high rpm also reduces the chances of carbon lock, which is like having carbon gravel bits bond along the sweeping surfaces and prevent the rotors from turning.

For a relatively new motor, I wouldn't worry about any of the above happening though.

northern-8

I agree completely!!! I alternate 2 tanks of 87 then one of 91 (the highest we normally have in Canada except for Shell and Petro Canada). I think that the one tank of premium is enough to clean things up.

I was always taught to use the minium octane fuel that doesn't cause pinging.

On both my Audi Allroad twin-turbo and my RX-8 I use 87 and have no pinging. When I did some testing, Premium gave me no better fuel economy or proformance!

The oil companies are raping us enough without having to fork over another 5% for nothing.

Ajax

The problem is, it doesnt always all burn up in time. In the case of a rotary, unburnt fuel is swept into the exhaust.

I wasn't saying that 87 burns more efficiently than a piston engine, I was saying it burns more efficiently than 91, 93, or whatever you want to use as less is generally wasted.

I have never heard any knock running low octane gas and I don't buy "cheap" gas. I always buy from Shell, Amoco, Chevron, Mobil...

affenage

I don't have it in front of me, but my recall is that it stated in the owner's manual to use premium, but low octane fuel WAS ACCEPTABLE, though it may result in poorer performance.
My feeling is that if there was ANY risk of engine damage (ping, early detonation) by low octane fuel, Mazda would not have discussed low octane fuel at all, and said to use premium flat out - with no disclaimers.
I have never used premium exclusively in any vehicle, and the Prelude I drove ran over 150,000 miles on 87. Honda says about the same thing Mazda does for the 8 - premium, but regular ok with possible lower performance. I think it's the mantra of the Japanese companies. I think that they are trying to make us feel we really are driving these "high end high performance" vehicles that require only the "best" gas. In other words - I think it's all a marketing ploy.
Certainly, tuned and running properly engines are RARELY if ever damaged by just the the use of 87 octane in this country.

johnmyson

Why not just compromise and use the 89?

HeelnToe

Hi affenage

It all comes down to compression ratio, boost levels, and the number of times a swallow needs to beat it's wings in order to maintain airspeed velocity.

But I digress.

As others have said, most cars have "knock sensors" these days which will compensate for lower octane fuel by retarding the timing (and lowering the max boost on turbos) when knock is sensed. So true, they don't get damaged, but they're also running in a sort of damage-control, "limping" mode.

If you drive a turbo car (like my old eclipse), you can REALLY feel it, as the CPU will just flat-out cut the boost on you. All the sudden you've lost 40hp, and you'd have to let off the throttle then mash it again to reset it. Awful feeling.

But normally, a car is designed to run at a partcular max timing advance (and boost level), which requires x octane to avoid the fuel going boom too early. Squeeze any fuel too much, and it eventually goes kaboom.

Now, since, high performance engines generally have higher compression ratios (or lower ratios but use a turbo to get the same effect), they need the high octane fuel to resist going boom from being squeezed so much.

The typical family car, which doesn't have such a high compression ratio, isn't as demanding (doesn't squeeze it so much), and can get away with lower octane.

Can you tell I'm having a slow day at work?

IMHO, lol, gearheads please correct me

affenage

haha me too wish the day was over and the weekend begun...
haven't lost any performance in the high RPM range on the 8 on the 87 octane yet, so far so good. I figure I'll notice that long before I notice early detonation problems

TRZ750

Can't belive all the TOTALY WRONG and partially wrong information being given out! Especially by dealer people.

Most errors are corrctly explained by other post, like octane, so I will not go further.

BUT "Furthermore, chevron's techron probably does nothing for the renesis as it's supposed to remove carbon deposits from the valves (in turn pushing them into the engine) but we don't have valves so what's the point?" IS WRONG!!!

Tecron or Tecroline is a very good cleaning agent for the ENTIRE engine. It cleans the fuel injectors and the rotary needs that. It cleans the entire combustion chamber and the rotory needs the spark plug holes, apex and other seals, and rotor face cleaned. It also cleans the exhaust system and actually helps the converter last longer.

Yes the higher octane fuels (as all fuels by current emision laws) have more cleaning agents (tecron or others), but you do not have to use these fuel to get the cleaning agents. Many fuel injector cleaners on the market use tecron, but usually at a low 5% mixture.

I work for Yamaha Marine and years ago (late 80's) we thought tecron was only good for valves and not 2 stroke outboards. Then we found out that customers using Chevron fuel (and others) had lower failure rates for ring sticking. After some research we came out with "RING FREE". This is a concentrated (above 50%) tecron (and solvent) mixture. Now, after over 10 years of marketing to outboard customers, we don't have to market this anymore as our customers and dealers have learned how much it helps a outboard. I started putting in one bottle in my cars every 6 month 10+ years ago and have already put some in my 8. My 89 astro van has 219K on it and uses no old and the throttle body injection looks brand new on the inside.

The only problem is when using on a old engine with a high treat rate is it can cause the carbon to flake off so much it will foul the spark plugs and cause the converter to run hot. So use low treats at first to slowly clean the engine inside. We have had a few cases where the fuel tank was dirty and all that dirt was cleaned by "Ring Free" and traveled to the fuel filter - pluging it.

You can see Ring Free at the www.yamaha-motor.com accessory web site for Outboards. Even our own motorcycle group can benifit from it, but doesn't activily promote it. So go to a Yamaha Outboard dealer. Use regular and every 6 months put a small bottle of ring free in the tank.

http://www.yamaha-motor.com/accessor.../1/detail.aspx

Nubo

Seeing as how the car has KNOCK SENSORS, I'd say it's a steaming pile.

RX8_Buckeye

This is flat out wrong! Dealer service doesn't generate any revenue for Mazda. In fact, Mazda loses money every time vehicles are brought in for warranty repairs. It's the dealers that gain. I'm amazed at the amount of horsesh*t being thrown around on here.

Vehicle manufacturers want to reduce warranty repairs as much as possible. They would NEVER specify service intervals that would hurt the vehicle. As the American car companies have learned, reputation is the most difficult thing to rebuild once you've damaged it. Sacrificing your reliability reputation to help the dealers make money is about the dumbest thing I've ever heard.

thew

Excatly, even a 2 stroke engine can ping. Valves have nothing to do with it.. and for that reason i say these guys are all full of crap..

The rev your engin till it screams idea is true.

I can vouch for this as this will be my 3rd Rotery, they need to be drivin hard. they luv it .

thew

hehe well, sorry to pop your bubbal. but its true . at least here in Ca, I have a freind at a Ford Lot here. hes a Heavy Mech, hes the guy that rips out your moter and stick in a new one.. he does no tuning, ... just the big stuff. anyway i have heard of many times that the Factory tells him to replace a part that could just be fixed cheaper and easyer , but the Dealership makes more money off a replacement than a fix !


What the factory wants, and what the Dealer lot provides is many times a much differant thing.

Look at our trbls getting the "m" flash. most deealers are just now saying " ok this is really ok with mazda", even though we all have read mazda's tsb telling them to do it to ever 8 they get no matter what ! ....

I wish it werent true . Good service is hard to find these days.