i've gotten into the habit of putting 89 octane gas in two fillups, then on the third fillup i use 93 octane. i'm a cheap bastard and prolly not doin any good for my car, but is there any real harm in this? gas in my area has been as high as $2.80 at one point, now it's around $1.35 a gallon. let me know. thanks.

 

i'm sorry. i'm stupid. delete this thread please.

 

no harm unless you're having detination at lower octane fuels

 

Your octane rating is additive and proportional to percentage of each type of fuel.

E.g., 5gal of 89 + 5gal of 93 = 10 gal of 91.

Running two loads of cheap to every one of good does nothing.