^now that makes sense mines an 06, ive been getting steady 15.2 daily, even with my recently added lift

 

Mine is 03 and I average 13.8-14.3 driving 95% city. Last weekend I drove Portland to Seattle and back, going average 75mph, averaged 18.1mpg

 

I have a 2003 and on last fill with 93 (Sunoco) at 90% city, I averaged 11.9 mpg.

 

Octane rating does matter. At the very least you are losing power. All modern cars have a knock sensor that will retard the timing when the computer senses engine knock. When you retard the timing you lose a little power. If your knock sensor goes bad and you continue to use the 87 octane gas you could end up with engine knock that can damage your engine. For most people losing a little power is not a problem. You should just be aware of what happens when you go with the lower octane gas. Then you can make an informed decision.

 

Update: just added E load heavy 285s, and im down to 14.9 average daily

 

I tried filling up premium gas for a month straight, and then went to regular. Never noticed any difference in performance or fuel consumption. So I just fill up regular 87 octane. If I ever tow or something similar, I'll fill up premium just in case.

 

What you are ignoring is that an engine with a compression ratio of 10:1 has absolutely no need for fuel with an octane rating above 87, and, with that 10:1 compression ratio, there should be no knocking whatever with 87 octane fuel.

As I said in an earlier post, I've had my GX since it was new in 2005. I have never used anything but regular 87 octane fuel. I have never heard a single engine knock, and I have consistently gotten 20 mpg (actually calculated) fuel economy in my driving, very little of which is in stop-and-go conditions, but, even if I was doing a lot of stop-and-go driving, I'm confident that my fuel economy would still be as good or better than what people using premium fuel are getting.

 

You're very lucky to get 20mpg in your way of driving. Just wondering which way do you calculate to get that numbers ? It's amazing !

 

If its less stop and go and all freeway commuting, that might be possible.

 

This kind of discussion can go on forever, we have so many threads exactly like this in the SC400/SC300 forums. I myself work on my own cars, I am very sensitive in feeling everything going on in my car while driving it, and I can tell a complete difference when using regular gas even in my old 95 SC400 which also requires 91 octane, and I felt it too soon as I got my GX. I would just tell people to just stick to whatever is recommended by the factory. It's not that much of a difference anyway in pricing. That's like what, $5-7 to the tank? There's really no reason to try and prove what the factory recommends is wrong.

 

^ totally agreed, i stick to 91, and its really not that much more for a full tank really

 

I seriously use 91 all the time since i bought my truck new in 2006, never try to use 87 or 89. For 2 years lately i've switched to 93 at Phillip 66 gas station that cheaper than 91 at Mobile or Road Ranger.
In winter i get 260-270 miles for 19 gallons including warming up the truck every morning .
In summer i get 330- 340 miles for 19 gallons without A/C in city and highway combination.

 

Just a quick update. 13.89mpg on my last tank. 95% in-town. 87 octane. No knocking and performance is fine.

 

Just bought an 03' and ran 2 tanks through it. I'm averaging 15.8mpg on my 3.5 mile trip to work in stop and go.

 

Here in Utah, 85 octane is regular, 87 is mid grade, 91 is premium. I wish 93 were available sometimes.

Mostly I run 91, but occasionally 87.