Gasoline Octanes to Use

OLERIM20

MEMBER
1997 FORD TAURUS
6 CYL
FWD
AUTOMATIC
140,000 MILES

I have a 1997 Silverado K 1500 4x4, Automatic, 5.7 Liter V-8 / a 2003 Ford Taurus SES, 3.0 Liter V-6 (Standard motor, not overhead cam), Automatic / and a 1997 Ford Taurus GL, 3.0 Liter V-6 (Standard motor, not overhead cam), Automatic ---- I have always heard to put 89 or + octance gas every few tanks to prevent engine gum up, but I wonder about getting the best mileage also. --- (All vehicles have between 115,000 - 160,000 miles, with the truck only used for pulling a boat or hwy driving when it is used and cars are some hwy/ mostly city driving --- What octane gasoline should be ran in each of these vehicles to prevent engine problems, get best mileage, and not waste money neadlessly on higher octance gasoline? Please list each vehicle seperately for different octanes suggested.

1 Reply

CARADIODOC

MECHANIC
33,870 POSTS

You're confused about the purpose of higher octane. The higher octane level makes the fuel harder to ignite. That prevents preignition and allows the engine to be tuned for higher horsepower. It does not provide or cause higher horsepower and it has nothing to do with keeping the engine clean.

Most fuels today have some ethonal added which is alcohol. Alcohol is a very good cleaner in itself. In fact, using alcohol in older cars can cause problems because it cleans the fuel system so well that all that gunk collects in the filter and plugs it.

GM has their own injector problems that no amount of cleaning is going to help. Chrysler is one of the few manufacturers that has almost no injector trouble at all. Ford falls somewhere in the middle of those two extremes. Octane ratings won't have any affect on how long injectors last. Unless the manufacturer specifies differently, stick with the less expensive 87 octane. If you hear any pinging under light acceleration, switch to the next higher octane. Understand too that GM uses knock sensors on most of their engines to reduce that pinging. When pinging is detected, the Engine Computer retards ignition timing which reduces power and fuel mileage. You may not ever know that is happening but your fuel mileage will suffer. If you find the mileage improves with a higher octane fuel, it is not because there are more BTUs in the fuel; it is because it is not necessary to retard ignition timing. The correct octane for each vehicle should be listed in the owner's manual. Don't waste your money on anything higher than called for.

Also, thanks to that Engine Computer covering up any noticeable pinging, it may be necessary to drive with a scanner connected that can read live data. It will show how many degrees of timing advance are being requested. If there is no difference between the different octane fuels, the higher octane is not needed.