Anybody actually read the small print on the E38 gas cap? I was surprised to see the following:

Recommended AKI 91
Minimum AKI 87

I'm going to run a tankful of 87 octane throught the car and see what happens. My '02 Maxima also has premium recommended but runs just fine on the "cheap stuff".

How will you know its running well on the 87? Higher octane is recommended to prevent detonation that might occur at lower octane. I don't think a manufacturer would recommend 91 if the car would run fine on 87 since there is no advantage to the higher octane other than preventing detonation.

If you do run 87 and start getting detonation you might not even notice unless you watching the timing and see the ECU start pulling it. I'm not saying its a bad idea to run 87, but I don't think you would immediately notice the drawbacks even if they are there.

How will you know its running well on the 87? Higher octane is recommended to prevent detonation that might occur at lower octane. I don't think a manufacturer would recommend 91 if the car would run fine on 87 since there is no advantage to the higher octane other than preventing detonation.

If you do run 87 and start getting detonation you might not even notice unless you watching the timing and see the ECU start pulling it. I'm not saying its a bad idea to run 87, but I don't think you would immediately notice the drawbacks even if they are there.

The car will retard timing to prevent knocks. I am pretty sure he will not get any knocks at all, though he will loose some performance.

In cooler weather you can likely get a way with it, but if its hot, I bet it will ping.

But really, why buy a 7 series and then put in the cheapest gas?

^
+1 Cause it says that in the owner's manual and when gas gets high in CA I run the minimum, and during the times when prices are much lower I run 91 octane

The car will retard timing to prevent knocks. I am pretty sure he will not get any knocks at all, though he will loose some performance.


You are right Cause it says that in the owner's manual and when gas gets high in CA I run the minimum, and during the times when prices are much lower or at normal prices I run 91 octane but I mainly run 91 octane

for maximum performance, you'll need 91 octane. Engine management is sophisticated enough that if it detects lower octane gas, it will reduce timing, resulting in less power, but no harm to the engine.

91 octane is selling for $2.71 at the Santa Rosa Costco today, anybody want to place bets on what it's going to be selling for this summer?

I understand all the hype from the manufacturers of these cars. Like I said, the 2002 Nissan Maxima documentation states that 91 octane is required for maximum performance but I've gone for months using the 87 octane and cannot tell the difference. I keep detailed fuel consumption logs on all of my vehicles and I can see absolutely no difference in gas mileage between the two octanes. Performance degradation is a hard thing to pin down unless you have access to a dynometer. Also, I bought the car (740iL) for cruising down the freeway so performance is not my main concern.

I have ODB software waiting at the office (I'm on vacation) that I'll be installing on my laptop to monitor the engine. I'm pretty sure the software will allow me to monitor timing among other things. If a slight loss of performance is all we're talking about it makes the argument for premium gas a little shaky, at least as far as my wallet is concerned.

Everybody is right - 91+ octane = max perf., also in higher alitudes, high heat areas (deserts)where cylinder charge is reduced. Most people dont run their cars max perf all the time. Between vanos and sophistication of fuel management system running 87 octane for commuting or on trips is perfically fine in keeping with manufacturer recommendations. If it pings there is probably something not working correctly. There is no harmful gum or carbon build-up going to 87 octane unleaded fuels. IMO its surely a personal choice. I ran low on fuel once in vermont and the gas station only had regular, i did notice the difference but took it easy and drove moderatly till i could get proper fuel. I have to use 91 min. - recommend 93 and i use same rule of thumb

Everybody is right - 91+ octane = max perf., also in higher alitudes, high heat areas (deserts)where cylinder charge is reduced. Most people dont run their cars max perf all the time. Between vanos and sophistication of fuel management system running 87 octane for commuting or on trips is perfically fine in keeping with manufacturer recommendations. If it pings there is probably something not working correctly. There is no harmful gum or carbon build-up going to 87 octane unleaded fuels. IMO its surely a personal choice. I ran low on fuel once in vermont and the gas station only had regular, i did notice the difference but took it easy and drove moderatly till i could get proper fuel. I have to use 91 min. - recommend 93 and i use same rule of thumb

I'm guessing you have to use 91 octane because of the supercharger, right?

Correct- but cruising at about 2800 rpm the vehicle gets better than stock mileage - turbo tronics upgraded software, - If u push it it hard u might as well just put the credit card on the center console.

but it has been said and documented that the car runs perfectly fine on 87... i have used 87 for both my BMW's and the last one had more than a few hundred thousand miles on the clock.

87 costs $2.20 in Nj where i just filled up, 89 was $2.37, thats a big enough difference that i dont care about the small diff it might make, and one which i dont notice when i do fill up with premium.

87 runs perfect and i cruse down the highway at 90+ mph, so i think i'll keep using 87 and most of the people on here will continue to use 91, what can you do?

This seems to be a long drawn out discussion. I am just wondering why people think the e38's V8 is high tech race motor when in all reality it is a 4.4L sedan motor with less then 300hp. I know guys with 700 hp turbo cars that use 87 so why shouldn't we; espcially when we our cars have a more advanced ECU.

Whats best for E32s?

but it has been said and documented that the car runs perfectly fine on 87... i have used 87 for both my BMW's and the last one had more than a few hundred thousand miles on the clock.

87 costs $2.20 in Nj where i just filled up, 89 was $2.37, thats a big enough difference that i dont care about the small diff it might make, and one which i dont notice when i do fill up with premium.

87 runs perfect and i cruse down the highway at 90+ mph, so i think i'll keep using 87 and most of the people on here will continue to use 91, what can you do?

True.

The most likely diffs would be some drop in mileage and, if pushed, some drop in performance.

Here is a link from Chevron (page 3 of 5): http://www.chevron.com/products/PRODSERV/FUELS/bulletin/motorgas/1_driving-performance/pg3.asp

an excerpt states:

"is difficult for a driver to know whether a gasoline has the antiknock performance the engine requires when the engine is equipped with a knock sensor system. These systems, which temporarily retard spark timing to eliminate knocking, are installed on many late-model engines (see Chapter 5, Gasoline Engines (http://www.chevron.com/products/PRODSERV/FUELS/bulletin/motorgas/5_gasoline-engines/pg3.asp#spark_control)). Retarding the spark reduces power and acceleration. The knock sensor responds so quickly that the driver never notices the knock. Loss of power and acceleration will be the only clues that the antiknock quality of the gasoline does not meet the vehicle's octane requirement. "

I am fascinated by this thread.
I had posted a thread on 1.3.07,with a poll asking if people used premium or standard, and the result was most everyone (73%) chimed in stating they were only using premium and that using standard was risky. Only 5 people said they used 87 octane!

Now it seems other people are stating the opposite. Where were you guys when the poll went up?
The debate goes on still, but if I knew from a reliable source that 89 or 87 would suffice, I might have to re-evaluate what I've been using...

the OCTANE question ranks up there with OIL WEIGHTS as one of the eternal debates

Despite the disagreement, it seems unanimously accepted that 87 won't damage your engine, so try it for yourself - run a tank of 87 and see if you can detect a difference, and if so whether you can live with it. The wrong oil weight, however, may damage your engine in the long term, so that can't be tested in action.

...and therein lies the dilemna.:devillook

If you run premium fuel 93 (R+M)/2 you will never have to worry about this stuff. The flame propagation speed is much slower and you will optimize your combustion. The knock sensors will not have to manage the engine map and your chances for long term carbon build up will be minimized. The extra charge per gallon of around 20 cents over say 100k and 5 years at 23 mpg avg is about $15/month extra.

As far as engine oil: I recommend only synthetic motor oils having a viscosity range of 5w-30 i.e. the BMWLL motor oil (non M vehicles); Mobil I 0w-40 or the AMSOIL 5w-30 or 5w-40 are some examples you can use in engines such as M50, M52, M60, M62, etc. You can run these oils in any car you own except for any vehicle having special viscosity formulation requirements and the M-series cars are the only ones I know having a greater viscosity requirement i.e 10w - 60 synthetic.

+1...I fail to see where there is any real dilemma. BMW states what they recommend for your vehicle...but then add that because of the knock sensors...you can use a minimum 87 AKI...but with decreased performance.

As its been said...if you can live with decreased performance (or even notice it in some cases)...the only risk is $1-$4 savings per tank at the most (that's if the price difference is .05 -.20 per octane upgrade from 87 AKI/89 AKI/91 AKI).

The 2001 M62TU engine is recommended to use 91 AKI fuel. If you don't want to pay the extra you can always use 89 AKI or 87 AKI and the knock sensors will compensate.

Where's the dilemma in that? :dunno

http://memimage.cardomain.net/member_images/1/web/433000-433999/433594_369.jpg

No dilemma for me, since I use premium for an engine that was designed for premium fuel. The wizardry of electronics will enable engines to run ok, but not optimally on lower octane fuels. I like to think about the whole system which also includes the catalytic converter and its lifespan. Certainly a consideration unless you are totally familiar with the combustion kinetics and can say for sure that using the lower octane fuel will not have long-term deleterious effects.

The folks in the forum can consider the following quote:

Premium gas isn’t cleaner, purer, or better than regular. The difference has to do with how it combusts. “Every vehicle is engineered for gasoline with a specific octane rating,” says Chris Thomas, the chief engineer of vehicle research for Honda Research & Development Americas. The recommended rating might be printed on the interior of your gas-cap door, or you can look in your owner’s manual. Most vehicles take regular unleaded gas (87 octane), but heavy trucks and high-performance cars often require higher-octane fuel (typically 91) because their engines have been tuned for extra horsepower. You’ll get no benefit from using a higher-octane product than the manufacturer intended. But if your manual calls for a premium grade, using something with a lower octane rating will reduce performance and fuel economy, and can prematurely age the engine.