DevTL

Hey why are you giving the guy such a hard time. Its a legit question. Last weekend in our local paper a nationally syndicated auto writer[s] stated that the octane doesn’t matter since new cars cpu's adjust. I don't believe it, there has to be some knock for the cpu to know to adjust. And there was another article about how lots of people are switching to lower gas and how gas station owners are not happy since their margins are better w/the higher octane gas. The gas station owners are worried that our habits will change permanently. The article mentioned a woman three series BMW, (and BMW named as “one of the manufactures specifying 91”), who had just driven away from the pump and getting 87. The Saudi's are also worried that our usage habits will change permanently. If prices decrease and we use less gas they are SOL. There are lots of people on this board that may have some actual knowledge on this issue. I’m glad the question was asked.

Btw, the mpg in the TL is great. Really why compare it to a civic? Why not compare to the other cars we compare to the TL on other threads, G35, M45, 530, 330 etc?

PenancE

lol, its a 1.02 for 87, i buy premium.......no supreme..

akm13tl

Actuary, stop being a fool and give your ride proper fuel. you are damaging the life of the vehicle engine by putting fuel which the car has not been designed for.

the diffference in price of a full tank is 2-5 bucks so why are you crying about gas prices ... like I said if gas price increase is making you cry ... go buy a hybrid

jhawk5

Back to the size of the tank.

As most have stated the spec size of the tank is approx. 17.2 gallons. Yesterday I filled up 15 miles after my "low fuel light" came on. I filled the tank to full and at the first auto. shutoff I pumped it up about $.50 to the nearest dollar.

When I was done I had only put in 14.5 gallons and upon starting my TL the gauge was above full. Thus from my calculations there is approx. a 3 gallon reserve in the tank ...........

(17.2 less 14.3 = 2.9 gallons)
( 14.3= 14.5 less .20 for $.50 to nearest dollar topoff)

brewtoo

My experience shows otherwise. Click here for Message 58 of this thread

And that is a car that doesn't even have a knock sensor.

Ron A

You are comparing a 14 year old car to a new TL. You cannot compare these because the computer and fuel supply system and electronic controls have come a long way in 14 years.

I used to run my 1996 3.2TL on regular when it called for premium and had no problem doing that.

If you run the 3G TL on regular, try this. Floor the gas pedal and see how far up the scale the tach will go. I can virtually guarantee that when it hits around 4,000rpm the Malfunction Indicator Lamp will come on and the rev limiter will kick in and you will not get that engine over 4,000rpm.

Think about what this might mean if you are passing and misjudged or someone pulls out in front of you and you need to execute the passing maneuver faster and your engine cuts out when you downshift. Might be unpleasant.

Edit note: And I remembered that I said this on the first page, but it bears repeating in light of this new topic.

Brettg

The only way the ecu has of knowing what octane rating of the gas you put
in the tank is if you get knocking that triggers the knock sensors.
There is no octane sensor on cars.

In cool weather, and/or light throttle, even low octane gas likely wont trigger
the knock sensors.
Hot intake air increases the octane needed to prevent knock.
On older fuel injected cars, the air intake temp sensor was used to retard
the ignition timing, on cars without knock sensors.
My 1990 Jaguar (4.0L inline 6) was set up that way, all the intake temp sensor did
was retard the ignition timing to prevent knock.

With modern cars having knock sensors, they use those to retard the timing.
Retarded timing gives less power, less MPG, and you could likely get light knocking
that could do damage over time.
You also have to have a knock for the sensor to detect, so you get SOME
knocking...
I dont know how often the ecu will adjust things, some knocking and you get
retarded timing till you shut the engine off?
Every so may engine revolutions?
Every so many minutes?

Ignition timing is important, I can feel the difference from small changes in
timing quite a bit on the motorcycle....

Brett

brewtoo

You are exactly right, cars back then did not have the sophisticated computer systems and knock sensors to protect them. And even so, our 1991 Mercedes 300E still runs great after fourteen years of a steady diet of 87 octane. So reason would dictate that it is even safer to run 87 in a modern computer-protected automobile.

I also own a 2003 Corvette Z06 (405 HP). Even though premium is recommended for that car, the owner's manual says 87 is also OK. I try different octanes in that car just to see what difference it makes and I don't believe I've injured it by doing so. It will spin those big tires into third gear every time and hits the rev limiter at the same RPM no matter what brand/octane fuel is in it. With that car, if you get on it in first gear, it winds up so fast it's very difficult to get out of first before you hit the rev limiter.

brewtoo

This makes me wonder, let's say you are running regular; the knock sensor hears the knocking and retards the ignition until it hears the knocking no more.

Now, let's say you are running premium; does the system still advance the ignition until it hears knocking and then back it off a bit?

If so, the engine would experience the same amount of knocking no matter which grade of fuel you used and would be equally "damaged" either way.

Brettg

With the correct octane rating, you should get no knocking at all.
The engine and ecu will be designed to work at normal temps and loads without
knocking with the correct octane rating.
You CAN use lower octane, under light loads, in cool temps, without knocking.
You will not be able to use lower octane if its hot out, and/or high loads.

Just how the ecu reacts to the knocking is what I dont know, I have no idea
how often it updates...

Since the manual says regular gas could eventualy cause damage, I suppose
the ecu updates fairly often...

Brett

tekageek

Well this sucks, went to a Citgo gas station yesterday and hit the 91 octane button to fill up. Didn't pay attention and was already up to $25 when I looked at it again and the 87 octane button was lit with the price.
Stopped the pump and went inside to see if they could figure it out. They had no idea.
One tank of 87 octane shouldn't hurt it, right?

Ron A

One tank won't hurt. I had to use all kinds of gas after Katrina and Rita. Put in mid-grade once, then the next time put in regular. You bought what you could get around here.

Just don't rev it all the way up and you will be fine.

Actuary

Gas price is bouncing again with no apparent reason week after Rita. I had 89 octane for 3 months now and havent had any problem at all.

I can tell 87 gives me less power and less MPG so I will stick to at least 89 for now.

mlody

My light came on today, I did about 20 more miles and barely filled it with 13.5 gallons of gas.

mlody

Since in Chicago area I can't find 91 anywhere, I have been altering between 93 or 89. Since my car requires 91, I believe that putting 93 is a waste of money. It is my understanding that octane mixes up really easy; altering between the two grades could effectively give me around 91 required rating.

On the other note, if you car was bought used, you never know what gas was before – when it comes to warranty work, how a dealer is going to proof you that you put 87 not 91? You can always make stupid statement that perhaps gas station was dishonest – we do not know that either, do we? I believe that octane rating is just a pure BS – it is easier to convince someone who paid $35k for a car that it requires 91/93 than someone who paid $15k for a car – that is why we have different ratings.

Giving some people crap about how can you afford $30-35k car is just pure ignorance – you can find a used ’04 TL for $26-27k or better ’03 TL-S for $21-24k – less than a new accord/camry/maxima/altima – some people saved for this car for few years (just like I did) and do not make $500-600 monthly payments, only $250-300, so spending extra $20-30 worth of gas a month is a lot – it is not a deal breaker, but I would rather spend this money on Friday night beer, or a movie ticket, or save it for another nice car in 5 years or so
What else can $25k get me? An ugly Altima, or Camry, or some domestic junk that won’t be worth $10k in a year because of employee discounts crap etc – I preferred a used car from a higher shelf.
The maintenance/parts on this car are as expensive as on a civic (besides the Brembo on the manual box) plus/minus few bucks here/there.
It is all about choices!

tejesh83

In my last car, 2003 Qx4, premium fuel was recommended (however the manual also stated the min requirement of 87). I ran some month long trials to compare octanes. With 87, I actually got slightly higher mpg. But it did "feel" a bit sluggish around town. I put "feel" in quotes because it likely could've just been psychological. The gas companies are good at brainwashing us to believe 93 is better (ie: the name Premium vs Regular). I would've been more convinced if I had measured results (time trials or dynos).

After the experiment, I still tended to use Premium. The gas companies marketing worked on me. But occasionaly on long highway trips, I refueled with regular since I couldn't really feel a difference at highway/cruising speeds.

There are a lot of good articles out there that discuss octane ratings and fuel additives. And this particular topic, Regular vs Premium has been beat to death. Basically, use no higher than what the car recommends, since the ECU will most likely not be tuned for it and so its just a waste of money. Use the recommended for best performance. If you use lower, the ECU will automatically and almost instantly retard the timing to prevent engine damage.

For now, I'm sticking with premium in the TL. I'll have to recheck the manual to see whether premium is recommended or the minimum requirement. But from past experience with the Qx4, I'm not too worried about using 87 in a pinch. But if one is using 87 to save money, you should probably compare mpgs to see if it actually works out in the long term. And since we're not sure how it will affect the MID, you should probably use the odometer/gaspump method for a good comparison.

mlody

I think most Nissans’ will say minimum octane 87 needed, but premium required for maximum performance. Acura lineup is a bit different because it says 91 octane required so really we have no choices.

mlody

Question to people who have 91 in their states - Is 91 considered mid-grade or is it premium. Is Chicago there are (in most cases) three kinds: 87, 89, 93.