The G Man

I think on the GX, it doesnt matter as much, you may lose a few HP. When you start going up over 11:1 compression ratio, thats when higher octane is a must.

BLKGX470

correct me if i'm wrong...did the octane preferrence on the manuals change after 2003? It says on my manual to use 87

ben_caron

Hello fellas and gals,

I have an '06 GX and there is a PREMIUM UNLEADED FUEL ONLY decal inside the fuel trap door.

Generally speaking The G Man is absolutely right. I asked a friend of mine who works for Nova Chemicals to explain to me why I should or should not use premium or super premium unleaded fuel in my bimmer. Here's the summary.

High-performance sports cars require high octane fuel because of the high-compression in the cylinder may cause lower octane fuel to ignite before the piston runs to its top-most position in the cylinder. The warmer the engine, generally the more it happens.The higher the octane, the higher the resistance to auto-ignition of the fuel due to compression or heat.

There are two reasons to use higher octane fuels: (1) towing, (2) higher quality additives.

Towing
Now for a truck like ours, you should see a considerable difference when towing, off-roading or if you live in the hills/mountains.
Why? Because the benefits of higher octane are typically felt when the engine is revving at the upper-end of its power curve. When the manifold is at max open position, there is no air restriction and very little vaccum. Typically when torque climbs (best power output), this is the point of highest compression in your engine, and using lower octane fuels, it is prone to knocking if the resistance to self-ignition is not high enough to cope with the compression in the cylinder. When we tow stuff, this can happen.

Now, most modern engines have anti-knockback features on the on-board computer, and they will tweak the engine to let in more air, less fuel (less rich combination), and delay the spark. What happens then? You lose some torque. Various tests have shown that you can lose 3-5% of your optimum HP & torque under such circumstances.

Additives
In general, additives and detergents added to premium and super unleaded fuels are of better quality. I remember some years back, Shell was subject of a class action by Montreal-based car owners because some additive found in the lower grade fuel was causing misfiring and damages to Chrysler engines. And yeah, Shell denied everything up to the last minute, but this time, they were caught with their pants down on this one.
http://www.apa.ca/template.asp?SectionID=3&ArticleID=13

There is however 1 circumstance where you should use LOWER octane fuel.
If you live in the mountains and drive in high altitude, for every 1,000 feet above sea level, atmospheric pressure drops by about 10 kilopascals. Thus, at 1,000 feet or above, 91 octane performs like 93 octane at sea level.

Now my rationale is quite simple. Why take chances? You can only gain by using higher octane fuel (less chance of dynamic de-tuning, higher compression achieved, generally better quality additives, etc.).

Cheers!

Ben

The G Man

I believe from 03 to 04, regular octane is all that is needed. The 05 engine went up in compression ratio due to the VVt-i engine which recommends 91 octane and 06 to 08 requires 91 octane. The main difference can be seen in the HP and torque rating between the GX and the 4runner V8 which has the same engine. The GX on 91 octane gets 263 horsepower and 323 ft-lb of torque and the 4runner V8 gets 260 HP and 306 ft-lb. As you can see, the big difference is the torque which will be noticeable when you are towing or climbing hills. Not sure what the diff. is to justify the 05 premium fuel recommendation to the 06-08 requirement of premium fuel. I think it is a marketing thing to differentiate the GX from the 4runner. In a higher compression engine, you will lose a lot more than 3 HP from using lower grade gas, thus losing gas mileage as well.
As far as Premium gas having more cleaning additives. That’s is only true for Shell and a few other gas companies. Most gas companies have the same amounts of cleaning additive across the board. You can always buy a bottle Techron fuel injector cleaner every oil change to get the same affect for a lot less money. Bottom line is, unless you tow, or climb a lot of hills. The HP gain from using premium gas will not be notice in every day driving.

vxphan

I am using 91 premium to prevent knocking when first start. There is a noticeable different when you go up hill. The engine is running smoother and quieter when uphill.

Cheers

ben_caron

Independent testing of fuels done by the "Top Gear" people on BBC.

http://www.youtube.com/watch?v=dDHwCWdrtdg

I just love this show!

anyone seen the one where they try to peg the best handling car in the world and professional drivers are having a blast with the peugot 105 hatchback? this was hilarious!

And now, if you think about adding "high performance" additives to your gasoline...think again...another good one from "5th Gear"

http://www.youtube.com/watch?v=O2KNbbdQv3E

Enjoy!

Ben

sirCharles

I use 93 octane for my girfriends GX. Just feels better.

munki3b0i

iTrader: (1)

i use 91 octane here in sunny ca, i did try a few tanks of 89, i didnt notice any performance decreases or pinging... but then i kept noticing that sticker on gas door so i switched back to 91. i guess it was a mental thing

redrocks

With gas prices going up, how many people are using regular in their GX?

From the owner's manual:

Fuel selection:
Select premium unleaded gasoline with an Octane Rating
of 91 (Research Octane Number 96) or higher for optimum
engine performance. However, if such premium type
cannot be obtained, you may temporarily use unleaded
gasoline with an Octane Rating as low as 87 (Research
Octane Number 91).

So other than not being able to achieve 8.1 seconds from 0 - 60, any other impacts?

BlairC

i run 92 consistantly.

easgx470

I run 89 now but mine is a 2004 (non vvti). Switched from 93 about 4 months ago with no difference.

Booyah

Its only money! It calls for Prem--It gets Prem!

snhrph

Since I own the truck and plan on keeping it for a while (my wife plans to run it into the ground), I use premium.

I have used regular on a couple of occasions while traveling in Canada, and did not have any issues or problems. I don't recall any noticeable decrease in performance either.

It boils down to individual "gas price tolerance"...

cssnms

Regular since the day I bought it. 64k on the clock and it runs like a top.

MWalker

Mine is a 2005, so premium is not required. 77k and runs great.