I remember reading in a thread recently (last week maybe) that you should always use the lowest octane recommended in the owner's manual - that there is no reason to run premium unless you are specifically told to (assuming you are normally aspirated). Something about pre detonation and the pistions I think, and that the higher octane was a waste - the technical explanation was a little over my head.

Anyways... I've been running 89 octane in my 96 4Runner (V6) for a long time. After reading that thread, I bumped down to 87 to save some cash. I know there are a zillion things that affect gas mileage, but between the last tank (89 octane) and this tank (87 octane), I'm getting about 40 less miles to the tank with 87. Driving habits and conditions are basically the same, so I have a hard time believing that at least most of the difference is due to the gas.

Could/Does octane affect gas mileage? I only save about $1.50 by filling up with 87, but the loss in gas mileage isn't worth it. Am I missing something?

 

Did you notice any engine knocking/pinging? If you had some predetonation with the lower octane that would effect your gas mileage.

 

Not that I nocticed... but I've got so many rattles in my rig that I keep the radio turned up pretty good, so I might not have heard the pinging. I'll drive home with the radio off tonight and see if I hear anything.

 

You should run a can of BG44K or something similar. Running the higher octane stuff for long periods of time can lead to carbon build up from using gas that has a higher flash point than what your engine needs. The carbon build up will increase your compression. Then when you switch back, your performance will suffer.

 

Use whatever is recommended for your truck. Newer vehicles are able to detect the octane rating and advance timing with higher octane for more power as well as retard timing if knock is detected. If you switched to 87 octane and you started detonating (and your engine has a knock detector) your timing may be retarded you prevent this dangerous condition and you would get suboptimal air:fuel ratio and less milage.

If you're getting detonation with the recommended octane, it may be carbon buildup as pistonslap says. Run some engine cleaner and maybe change out spark plugs.

Pitchar

 

I personally have notice a major diference in power from running premium fule in my 91 4runner with the 22re. Mabe it's all in my head but I swear I can pull hills better with it. I also seem to get about 1 to 2 mpg better milage than regular. Am I on crack or does it actually give you more power?

 

Predetonation will hurt your power, so if switching to premium stops you from getting predetonation, then yes, it will give you more power. The higher octane fuel is actually less volatile than regular so I can't see it giving you more power unless the regular is too volatile for your compression and is exploding before it gets a spark from the plug.

 

I have a related issue to add to your topic about fuel. My 4runner has a check engine light that pops on and off. I began to notice that it would come on for about 4 days, then it would go off for about 6 days, usually spanning the weekend. Then I started to notice that it would come on after I put in 87 in the tank from Kroger Gas pumps. Sometimes I would get shell gas and it would come on. Then I decided to get 89, and it didn't come on for well over a month, regardless of where I purchased it. Then I got it to come on once after a Kroger fill up again. It stayed on the duration of the tank. Filled up with Kroger 91, and after 15 miles, it went off and hasn't come on since. That was about 3 weeks ago. So it is either Kroger gas, low octane gas, or both. And I have the rotten eg smell from the converter. It got much better with the better octane fuel. My fuel milage hasn't really changed much, but the car doesn't seem to hesitage as much crossing over 3K. It was like it would almost stall. Now the runner seems pretty fast, with only the slight smell of rotten eggs!
So premium fuel helps me.
Wes

 

What year is your 4-runner Wes?

 

I just recently switched from 89 to 87 too but my mileage has stayed the same. Maybe even a little better city wise too. Ive also noticed that I seem to get a bit more oomph but thought it was all in my head. No engine pinging either so I think I'll stick to 87 at least til something goes wrong.

 

This sounds a lot like the ECU through a knock sensor code.

I'd be tempted to suggest that you do what you can to get the light to come back on, then head to a Schuck's or AutoZone and get them to read the diagnostic code. I bet it'll be a knocker.

If it is, then toss in a bottle of an octane booster and you won't have to spend the rest of the tank looking at the light.

If it's not, post the code back into this thread and we can help you figure out what's really happening. The point being that you shouldn't have to run premium fuel in a stock engine. You're treating a symptom of some other problem.