Gas Mileage Reg/Premium

[Rodjaxx]

I just ran a MPG test on my wife's 90 Riv. I filled it up with Reg gas last month, set the trip and noted the price of Reg @ $1.999 and Premium @ $2.199 a gal. Week befor last filled up with Premium and took the # of gal. x $1.999 and that cost was divided by the miles driven (all in town,milk store,post office, ect.)for a cost of $.1196 per mile. Today I filled up again and took the # of gal. x $2.199 and that cost was divided by the miles driven (all in town,milk store,post office, ect. again) for a cost of $.1108 per mile.

I did this back in 1999 with my, then new, 1998 1 ton Chevy truck on a trip from Seattle to St. Louis with the same results (it seems 2 or 3 cents better)

[Shelby]

Statically Speaking,

That is a pretty small sample to go to 4 digits.

[Guest imported_barra]

I have had two '89s, my current '88 Reatta and a '92 Riviera. I have run them all on premium and regular gasoline and have seen no significant difference in mileage per gallon or driveability. How efficient they are seems to rely on the condition of the ignition and fuel injection system. No insult intended here. There are just too many variables like time spent idling in traffic, weather that requires air conditioner/defrost or just having to get out of someone's way to avoid an accident that alter your test results.

[padgett]

There is no difference in BTUs (energy) per gallon between regular and premium (if anything premium is lower). The difference is an additive package that makes premium slower burning and raises the flash point (to avoid detonation).

Since the Reatta is designed for regular, the spark maps would not have enough advance for premium (slower burning) and a good running engine will not get as good milage.

Now if the engine was running poorly and there was a lot of knock retard (see OLDPA3) being dialed in then maybe.

My last tank (~120 miles to Titusville and back with a/c, ~100 miles around town, regular $2.099/gal at Sam's) was 23.2 mpg

[Guest tempest68]

I find it interesting how few people really understand the difference between regular and premium gasoline, and what it means for today's computer-controlled cars.

What Padgett describes is right on the mark (I dont think I've ever seen Padgett be off the mark).

I really did not understand the difference until two years ago when we first bought our GTP. Because it requires 91 octane or better, I started researching why.

I wonder if everyone stuck to the 87 octane that is the minimum/preferred gas for most vehicles and only those people with cars that truely required premium bought premium, how much higher would the gas companies raise the price of premium over regular due to low demand vs. cost of producing.

[Guest imported_barra]

Refining petroleum into other products is a"cracking" process that once begun must follow until all of the crude is distilled to everything from asphalt to "casing" gasoline- so volatile that a cupfull poured out will evaporate before reaching ground. I do not know what the percentages of distillate are at each stage. Perhaps that is the reason for a price difference - that and the additives that affect the flash point and rate of burn.

[Guest Buick Mike]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">

I wonder if everyone stuck to the 87 octane that is the minimum/preferred gas for most vehicles and only those people with cars that truely required premium bought premium, how much higher would the gas companies raise the price of premium over regular due to low demand vs. cost of producing. </div></div>

I have a friend who would always fill his Jeep truck with premium. I tried to explain that he was wasting money, but he swore that without premium the engine would knock and run rough.

OK, whatever.

So, as it turns out, I end up buying the truck and guess what? I never put a single drop of premium in it and it runs just fine on 87 octane.

The mind can be a strange thing.

Mike

[padgett]

As Will Rogers once said, "It's not what people don't know that is the problem, it is what they do know that's not true."

[2seater]

How do you remember all that good stuff?

[Guest tomt]

Read your post, but noted at bottom you are looking for an 89 Red and Gray. My Buick Dealer has one for sale I believe still, as I saw it while he was working on my car yesterday. As I recall, it is about 87,000 miles. I believe this has been his car since new, he's just clearing the garage. Don't know if he still has the other, but he did have a white 90 convertible as well with about the same mileage. Interior driver door panel damaged. The coupe has 16 way.

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