26 Apr 2005, 16:04, JIM HOLSONBACK (1:123/140), wrote to ALL:

Hi JIM.

 JH> Hello, ALL.

 JH> Our 'family' car here is this older Buick sedan - a '98 LeSabre. 
 JH> Engine is the GM 3.8L V6. (I've had several cars with this block over 
 JH> the years, with generally good service).  IMO it gets decent gas 
 JH> mileage on the recommended 87 octane. I bought gas here last week at 
 JH> Costco, and it was 2.03 for 87 and 2.13 for the 91 octane. (A bit less 
 JH> than 5% price premium). This is unlike a lot of the commercial gas 
 JH> sellers, where the high-test is typically $0.20 or so more than the 
 JH> regular.

 JH> I don't take many long trips, mostly local but not much stop and go
 JH> in heavy traffic. I was thinking if I'm averaging 20mpg now, and 
 JH> could get 21.0 or better with the higher octane with my type driving 
 JH> of it, I'd be doing OK.

 JH> I'm surprised I haven't seen any articles about this situation. My 
 JH> question- might I be able to get more than 5% mileage increase if 
 JH> I start running the high-test?

You _might_.  Modern engines have anti-knock sensors built into the engine
block to 'listen' for detonation and retard the spark timing accordingly. 
If by using a higher octane fuel the anti-knock sensor fails to 'hear'
detonation, then your onboard computer may let the engine run at a higher
timing advance, which would improve your mileage.  Even one or two degrees
additional timing advance should give you improved mileage in the range you
seek.  

You would have to maintain careful records though, and calculate the cost
differential to make sure the difference is worth the effort.


     Good luck...  M.

--- Msged/386 TE 06 (pre)