I see this exactly as you do. Although the 6th gen simply RECOMMENDED premium, and has been proven to run fine on regular, the '09 seems more insistent that premium ONLY is to be used. Because the '09 does have a higher engine compression ration, I would not risk using anything but premium in an '09 until we have more specific information.

Having said that, Channel 2 (WSB) in Atlanta had several technicians on live during the period from late August until early October, during which premium gas was not available in the Atlanta metro area, and the Nissan tech said any Nissan would run fine on regular UNTIL premium was available again.

And having said that, I'm not sure I trust the tech to know the full story, and he didn't say whether regular might cause a little problem of some kind. I would play it safe and use premium in the '09.

 

Light, what you state WAS true in the days before knock sensors and computer controlled ignition timing (or in a lab test where ignition timing is not a variable). In the days of fixed ignition curves, if there was no knock, there was no point in using premium fuel. There is nothing inherent in premium fuel that would deliver more power or MPG under those circumstances. HOWEVER, the return of high compression engines coupled to knock sensors and variable ignition timing has introduced a way that octane CAN effect both torque and efficiency.

Higher compression ratios are directly related to higher torque output at lower fuel consumption rates, so engine designers like higher compression ratios. Like everything else, higher compression ratios have a downside: the higher cylinder pressures they create increase the likelihood of destructive knocking. In comes higher octane fuel to the rescue... its higher resistance to knock - its ONLY redeeming quality - keeping engines from self destructing.

Now everybody is happy, EXCEPT that premium fuel might not always be available. So modern engines are equipped with a secondary defense against knocking.... retarding ignition timing to lower cylinder pressures, initiated when microphonic sensors detect knocking in progress.

What effect does retarding ignition timing have? It REDUCES torque and INCREASES fuel consumption, throwing away the gains in that area created by the higher compression ratio in the first place.

If you are using regular fuel in your high compression, knock sensor equipped Maxima, just because you haven't heard knocking doesn't mean that it didn't occur... the knock sensor just heard it first and the engine went into self preservation mode, retarding ignition and, inescapably, reducing torque and increasing fuel consumption.

In the end, cars that recommend premium fuel are just giving you the choice of either allowing the fuel to prevent knocking in the first place or to rely on compromised ignition timing to suppress the knocking when it inevitably occurs. What makes the most sense for a particular driver depends on a few factors, but mainly on the price differential between fuel grades and how often the car is driven in under knock-conducive conditions.

If you are running predominantly in steady state highway cruise mode, save your money and use regular fuel because you are not likely to be creating much knock under those conditions. The best candidates for taking advantage of premium fuel are economy minded MT or CVT drivers who short shift in low speed traffic and allow the engine to run under high load at low engine speed - prime knocking territory. Everything else falls somewhere in between.

BTW, the removal of the word "recommended" in the 7G's premium fuel requirement statement indicates that Nissan has pushed engine parameters sufficiently far enough - to increase both output and fuel efficiency - that ignition retardation may no longer be sufficient to prevent knock under everyday driving conditions. Personally, I wouldn't think twice about using anything but premium fuel in a 7G. However, if your driving conditions are not particularly conducive to knock, you might get away with regular or mid-grade fuel. I'd recommend listening awfully closely for knock if you make that risky choice.

 

Very informative. Thanks.

 

Getting alot of good info here, I added it to the stickies.

 

i've used 87, 89, 91, n 93, i felt no power difference, however gas milage were different, non of them hurt my car... i thought the difference in grades were that the lower you go the faster it burns

 

Exactly... slower burning of premium is what keeps the knocking in check.

 

Grand_Hustle, good info, but do you have an 09 where both the users manual AND the car state "Required"

 

jcalabria - Very informative post. It seems technology has finally left me behind. Maybe I can go back and try to rebuy my old '49 Studebaker; at least I knew how that baby worked.

Your post definitely reaffirms what I have posted in several threads here: don't use anything but premium in the '09 until we have definitive info it would be OK to do so. After reading your thread, I certainly would not consider using regular in this higher-compression '09.

Thanks for the info.

 

I filled up with premium!!! lol!!

 

I don't understand. Couldn't Nissan just have two different programs? One for Premium and one for Regular gasoline?

jcalabria, that was an excellent post. I can most definately feel a difference when I put in regular fuel in my M35x. Torque seems to be the most affected when using regular fuel.

 

That's essentially what they have done, except that by using the knock sensor to activate the "regular" ignition program they avoid having the timing compromised all the time. This way, using regular grade fuel does not require the ignition retardation 100% of the time - only if and when knock is sensed. If the retarded ignition was triggered by the gas itself, they would be retarding the ignition full time and fuel mileage would tumble regardless of driving condition/styles.

What I feel most when I use regular gas is a sense that I am pressing the gas pedal a little further for the same level of acceleration during part throttle roll-ons (accelerating on on-ramps, etc) - especially during very hot weather. This is exactly what you would expect knowing that those conditions represent prime knock territory and that the resulting spark retardation is cutting the amount of torque produced, and you end up feeding more fuel to compensate for the retarded timing. I find this especially an issue with the CVT, because sometimes that little extra bit of throttle causes the TCU to think you are being more aggressive than you intended and you end up with a lower ratio and higher RPM than you wanted (and the dreaded droning sensation). It's easier to keep the engine running at lower RPMs with a more linear throttle response when the motor has that extra bit of torque to work with.

 

Come on now... I know you wouldn't give up your heated steering wheel!

 

I did 91 yesterday and it feels fine. I'm going to up to 93 starting in my next fill. The tank is BIG..well big compared to my old 99 Z28. Half a tank cost me 44 bucks, but it gets much better mileage. I could probably fill up once every 2 weeks or even longer.

 

Of course I couldn't give up the heated steering wheel. Not with my gnarly old wrinkled, bloodless, lifeless hands. I would simply buy the '09 Maxima, swap steering wheels between it and the '49 Studebaker, then donate the '09 Maxima with its old battle-worn Studebaker steering wheel to the Salvation Army. At least that old Studebaker steering wheel has a neat bakelite (forerunner of plastic) speed-steer **** attached, which should enable the already quick-steering '09 Maxima to be turned lock-to-lock in two tenths of a second.

My salesperson called today while I was out thinning the pines in our east yard. I have a feeling the sinking economy is making my offer on her '09 Maxima look a little better every day. I may wait nearer the end of the month to return her call. They always seem a little more desperate around that time.

 

I think if you put that small diameter '09 Max wheel on your manual steering '49 Studebaker, the effort needed to turn the wheel alone would get the blood flowing in your arms and hands. Good thing... I'm not sure how warm the heated wheel is gonna get with that 6 volt electrical system.

 

Thanks jcalabria. It makes sense that the knock sensor would detect the knock and switch to the regular ignition programming. I guess it switches back to the advanced ignition program when the vehicle is refueled (maybe some sensor in the fuel filler door)?

mls277, you do not need to spend the extra money to upgrade to 93 octane as it would probably do you no good. Heck, if I had gas stations in NJ that offered 91 at a lower price, i'd jump on it.

 

May I ask how much you offered them?

 

There is a very common misconception about cars "adapting" to fuels... The car does not ever know or care what type of fuel is in the tank. It always assumes its gonna be fed the good stuff and runs in the optimized "premium" timing mode UNLESS knock is sensed. When knock occurs, it instantaneousy retards the timing until the knocking stops. Once the knock is quelled, it will almost immediately attempt to return the ignition timing back to optimum settings (unless knock reoccurs). If conditions have indeed changed (e.g., you reached cruising speed on the interstate after your knock-inducing run up the on-ramp), the timing will return to its optimum mode almost immediately.

At least regarding ignition timing adjustments, the car does not ever "adapt" to a particular fuel, nor does it "take a few tanks" to adapt... Fully advanced is the "normal" mode and all changes from that are instantaneous in response to knock and immediately return to full advanced when the knocking stops.

That said (and I hate to bring this up and complicate matters, but...) there is a another method by which the ECU can deal with knock besides retarding the timing. The presence of knock is but one among a host of parameters that can effect the amount of fuel being metered into the combustion chamber. When knocking is detected, the ECU can richen the fuel mixture, cooling the combustion chamber but also sending unburned fuel out the exhaust... not good for fuel economy.

The ECU has two "windows" of adjustment range for the fuel mixture map... a narrower short term window that provides a range of fuel mixtures at any given time. Fuel mixtures are instantaneously adjusted within the short term window to deal with current operating conditions. There is also a larger long term window that is primarily meant to deal with seasonal changes. The whole short term window moves slowly within the long term window, keeping the "average" fuel mixture requirements currently being called for in the center of the short term window.

Although this shifting window system is primarily intended to deal with seasonal requirements, prolonged use of regular fuel under knock-friendly conditions could potentially shift the short term fuel mixture window towards the richer end of the long term window, and it can take several days of operation under altered conditions (e.g., no more knock due to switch to premium fuel, etc) to move the short term window back to "normal". I suppose that this fuel map window shifting process can be considered an "adaptation", but it is still not in direct response to the fuel itself - only to the prolonged presence of knock (along with ambient temperatures, etc).

BTW, I do not know know which of the two methods - timing vs. fuel mixture - is the primary knock suppression method. The service manual I got this info from explains how each system functions independently, but does not state whether one method occurs before the other or they are simutaneously deployed. I suspect that it would be the timing adjustment, but cannot verify this.

 

Well, I sure learned a ton in this thread. Thanks jcalabria.

 

I doubt that there would be any difference in operation between 91 and 93, as 91 was the design target (just like it is a waste to use 91 in a car designed for 87).

If you have a choice in your market and there is a price premium for 93, it probably will not be worth it. Here in Charlotte we really don't have a choice - all I ever see is 93.

Also, did you figure your "half a tank" by the amount of fuel you put in or by the fact that the gauge was at half when you filled it up? In most cars, the gauge is not linear, with the upper half being larger than the lower half. Since a great number of folks always fill up when the gauge hits the half mark, the car companies think they are pulling a fast one on us and are making us think we are getting better mileage because we go so far on only a "half" tank.

 

For people who are having hard time finding 93 octane I suggest you add 32 ounces of xylene and you can feel a boost it is used in octane boosters and also used in bringing up the octane levels to 91 and 93 should not be used constantly because the blends are difficult to achieve and for that just buy the 93 octane. I used on another car also it will clean up the lines the injectors spark plugs. Some people use heavy dosage to race but it can cause damage. Try it out it worked for me.

 

I always get premium, 91 octane is the highest I ever see, but the real thing is whether I'm getting the 10% ethanol blend or the 100% gas. I have to drive a little further to get the 100%, but I think I'm going to keep with that because it seems to get better mileage.

 

i understand feelling a differnce but how do you SEE a difference in 87 and 93

are you refering to price

 

i think he is talking about MPG difference 87 and 93

 

We use minimum 91 octane in our '07. Dealer says it will run on cheaper gas, but power and mileage will suffer, so whats the point?

 

MaxMus - I offered $35,000 for SV with Premium package, Tech package, Floor & Trunk Mats, Splash Guards and Trunk Organizer/First Aid Kit. MSRP is $38,485. My offer is right at invoice. Despite their foot dragging, I feel confident it will be accepted with maybe some negotiating.

 

Hi Light, the car i'm looking at purchasing has a MSRP of $38,165 (SV with Premium and Tech, + Floor/Trunk mats). The invoice on that is $34,728. Do you think around March of next year, I can go in and offer $33.7 or do you think that is too low of an offer?

 

Hey Light... Check this out:They could have just hired some oldsters like us instead of subjecting this "kid" to the simulated effects of aging, lol.

(I know, off topic but the comment that inspired this was already in this thread)

 

I'm not the authority here on what might happen if you waited till March and offered the dealer a price more than the amount of the dealer holdback below invoice. I would think the dealer would have to be very desperate to either make a quota or get rid of the car to go to $33,700, unless the car had been test driven several months and had a few hundred on the odo. I did see a few deals like that on manual transmission Maximas back in the 2000 to 2006 period, where dealers were almost ready to push the manual tranny cars into ponds to clear the lot spaces for cars that would sell.

There will be different opinions on this, but I personally feel the absolutely dead economy has forced the dealer's hands, and they are already reluctantly beginning to deal near invoice on the '09, and it might well be that you could wrangle them down to very near $34,700 this month. By already dealing near invoice this early in the new generation, dealers have left themselves very little negotiating room going forward. I would think that even waiting until next March would not bring the price of the vehicle you want below $34,000, unless it has a few hundred on the odo.

Your best bet by far would be if Nissan offered some kind of incentive, which they may do during this horrible economic period. A rebate of $1,000 would put you at $33.700 without the dealer having to go below invoice. Otherwise, unless the dealer is desperate for whatever reason, even waiting till March, it still might be tough getting below $34,000. Just my opinon.

 

jcalabria - Automobile advertisers have always tried very hard to associate their products with young, vibrant, upwardly mobile achievers. But carrying this theme to the point of using one of those media-friendly yuppies to simulate someone in my advanced state is somewhat insulting. The kid isn't even showing the severe pain that would inevitably be on the face of someone my age in that awkward position. His feet are both pointing straight forward; at least one of mine is invariably pointed in the wrong direction for whatever I am trying to do.

At least with the Maxima, we have a very comfortable car for any normal size adult. My two 1985 Maximas had sunroofs which came close to my head, but still cleared by an inch. All Maxima gens after the 2nd have had ample room for me in all four seat positions. The '09 is especially accomodating, and I found it very easy to enter/exit. I really love the way Nissan indented the lower two-thirds of the back of the front seats on the '09, giving plenty of knee room for back seat passengers, even though the front and back seats are actually closer to each other than with the 6th gen.

 

I have had my ride for a month now and have filled up twice with 93 only, I did not want to spend $35K+ for my car and not feed it the proper fuel that was recommended by the manual. I figure just like everyone else is saying it is only about 4 bucks more a tank to ensure your baby is taken care of!

 

I filled up for the first time today after having the car for a month, and i used premium 92 octane.

 

I have noticed that the engine or the CVT(?) sounds "quieter?" since I've been putting in the premium? Is that possible? all I know is that the stars have been aligning for me with premium prices going down.

She moves like a bat outta hell with its BUTT on FIRE!!! lol!!!

Also I stopped using the thigh extender and the seat feels better to me. Felt like I was hanging off the seat where it separates.

 

Generally run 91, but I've done 89 in a pinch if the higher grade wasn't readily available.

 

Let me get this strait... You purchased a $40,000 dollar car and want to cheap out by putting 87 in it???? Why don't you open up your fuel door and READ what it says on the inside? Enough said....

 

Your kidding me right????




edit: thank you jcalabria!!!!

 

Drdla - from around 1949 until fairly recently, octane was not related to MPG. Higher octane was needed for higher compression/performance engines in order to prevent knocking and to obtain maximum accelleration, but (despite urban rumors), did not give higher MPG in a properly tuned engine.

But jcalabria has convinced me that with recent engines it may be possible to get very slightly increased MPG with premium gas in a high-compression engine designed for premium gas. BUT NOT ANYTHING AS GREAT AS ONE MPG PER TANKFUL.

The important thing jcalabria has shown us is that the engine on the '09 Maxima DOES need premium gas in order to perform as it was designed to operate. In order to run on regular, it has to make adjustments/compromises that mean it will not be operating at optimum efficiency. Because of this (and not because of a possible miniscule nudge in MPG), I will not be using regular gas in my '09.

 

no i own the car in my sig but IIRC im suppose to use 91

 

i use to work at carmax n iirc all cars were filled with basic grade gas no matter how new... $50,000 jag with 87 octane... it doesnt kill your car, it just goes into, basically safe mode, n take away lil performance

 

My 06 only gets premium and the 2 times the gas attendant filled it up with regular, I thought I had a hole in the tank

When I was a tech, many cars with rough idle, hard starting or stalling out after start up, all usually happened on cars that should have been running on premium with about 40-60k give or take, also depends on normal driving conditions, the simple fix was usually a fuel injector service and telling the customer to run premium

Also anyone running premium should never have to get a fuel injector service but calculate your mileage and you will always know where you stand.

What they should really do is advertise 2 or 3 ratings so that if the customer wants to put regular in the car over premium they can actually see a difference, these cars cost millions if not billions in the pre-production phase, Im sure they put everything in them from 87-93 and every other grade available