Back when the GMC was built the formulations of gasoline were much more rob=
ust. Todays gasoline is somewhat less, with the addition of ethanol (10% +=
/-) to the gas and it is true that the 10% addition of ethanol results in a=
drop in fuel mileage. I have driven almost 110K miles over the last 20 ye=
ar and noticed the different. Out West you can find more gas station that =
sell =E2=80=9CReal=E2=80=9D gas without the added ethanol and would sometim=
e run it when we were going into the mountains, but be careful a lot of rur=
al gas station sell an 85 octane Farm Gas. You do not want to buy that! Y=
ou can find =E2=80=9CReal Gas=E2=80=9D at boat marinas and at some gas sta=
tion that are around lakes and waterways but expect to pay a premium for it=
. My brother on occasion used to use regular pump gas in his boat, but fou=
nd out that was not a good idea. The ethanol is hydroscopic and absorbs wa=
ter and because of that he had his fuel filters plug up and fill with water=
. Do a search for =E2=80=9Creal gas near me=E2=80=9D and you will find a l=
isting of gas station that do carry ethanol free gas. Back to what gra=
de you can run? 87 octane is the correct for you GMC and will run without =
issues. If gasoline gets down on price I sometimes put some Mid-grade, typ=
ically 89 octane. Believe what Jim H says on backwater gas station and=
only buy a high volume stations. One other thing is if a stations tanks a=
re low you could possibly get some water and trash that will play havoc wit=
h your fuel filters. When most station stick their tanks for level that al=
so have a chemical that indicates possible water at the bottom of their tan=
ks, this is typical with low volume stations. The stations in tank pumps d=
o not pick the fuel up at the bottom of the tanks. The newer tank systems =
have a water sensor installed along with electronic level gauges. Rega=
rds, J.R. Wright GMC Great Laker MHC GMCGL Tech Editor GMC Easte=
rn States Charter Member GMCMI 78 GMC Buskirk 29.5=E2=80=99 Stretch 7=
5 GMC Avion (Under Reconstruction) Michigan > On Aug 22, 2020, at=
1:22 AM, James Hupy via Gmclist wrote: > > =
Chevron 87 octane swill gas. (Alcohol) or Top tier Costco 87 octane > reg=
ular. Buy from a busy station on major routes. Not some backwater > stati=
on. Fresher is better than aging on gasoline. > Jim Hupy > Salem, Orego=
n > > On Fri, Aug 21, 2020, 10:17 PM Vadim Jitkov via Gmclist < > gm=
clist> wrote: > >> Hello All, >> Just wondering what=
is the proper fuel grade to use on our GMCs. My >> understanding is that=
the 455 engine was originally built/tuned to run on >> high >> octane =
leaded fuel. What is a proper grade of modern fuel to use on these >> eng=
ines? I'm referring to the gasoline which likely have Ethanol added to >=
> it, i.e. plain regular vanilla variety gas station fuel. In my area ther=
e >> is no Ethanol free gas available, unless I go and siphon some from t=
he >> airplanes at the local airport :d Let me know what you all fill u=
p with. >> Thanks. >> -- >> Vadim Jitkov >> '76 Glenbrook 26' >> =
Pullman, WA >> >> _______________________________________________ >>=
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