Premium Fuel or Not...

[cadillacjeff7777]

Ok, I have always put premium in my cads but note the other day that it does not say Premium Only on the dash or on the fuel door. Do these cars still require premium? What is your preferance.

[Texas Jim]

In my particular car... using premium results in about 10 percent added fuel mileage and a little bit better performance.

Since my mileage drops about 2 MPG... from 22 to 20... when I use Regular... that equals 40 miles "LESS" that I can travel on 20 gallons of fuel.

That equals TWO extra gallons of regular at close to 4 bucks each or 8 bucks.

Since the price difference in regular vs Premium is about 20 cents a gallon... 20 gallons of Premium vs 20 Gallons of Regular is only about 4 bucks more.

Based on that... it is cheaper to use premium vs using regular.

In my owners manual on page 5.5 it says this about fuel...

Use premium unleaded gasoline with a posted octane

rating of 91 or higher.

You may also use regular unleaded gasoline rated at

87 octane or higher, but your vehicle's acceleration may

be slightly reduced, and you may notice a slight audible

knocking noise, commonly referred to as spark knock.

That being said... after several tests during road trips... I only use Premium...

Remember... this is in MY car... yours may be slightly different...

[JimD]

Preference is one thing, fuel cost per mile is a different beast.

And it requires a long term analysis of YOUR MPG to come anywhere close to an accurate fuel cost per mile using different fuels but discounting the fluctating price per gallon. A one or two tank test will not provide a reliable number. Excel is your friend.

For example where I live, 97 octane is $3.84 per gallon today.

89 octane is $3.99.

93 octane is $4.03.

Expressed another way, the cost per gallon of 89 octane is 3.91% higher than the cost per gallon of 87 octane. If my MPG with 89 octane is also 3.91% higher than my MPG with 87 octane, the higher octane is NOT costing me any money.

And by only considering the percentage difference between the prices of the two fuels, the actual pump price is factored out.

[rockfangd]

I completely agree with all you have said. Also given the quality of todays fuel. I only run premium in both of mine

[jje1953]

I completely agree with all you have said. Also given the quality of todays fuel. I only run premium in both of mine

FWIW - My 98 Deville specifies 91 octane premium, but here in Nebraska, Premium is 40 cents a gallon more that 89 octane ethanol blend. Been sampling the 89 ethanol blend, and have noticed no drop off in fuel economy or power.

[KHE]

I completely agree with all you have said. Also given the quality of todays fuel. I only run premium in both of mine

FWIW - My 98 Deville specifies 91 octane premium, but here in Nebraska, Premium is 40 cents a gallon more that 89 octane ethanol blend. Been sampling the 89 ethanol blend, and have noticed no drop off in fuel economy or power.

40 cents more per gallon - OUCH.

I run regular in my Northstars and have not noticed any performance or fuel economy loss.

[Dr.Fiero]

Best fuel we can get here (which I have always run in my '98 - Chevron 94 octane) is $1.55. Per Liter. Which is 5.86/US Gallon.

So I'll hear no grumbling about high prices.

(I'm sure someone from Europe will now chime in about what THEY pay!)

That aside....

If you drive gently (keep your foot out of it), then higher octane is somewhat useless, and you're paying for nothing.

If you DO drive hard and run low octane fuel, then you'll get more knock, the ECM will pull back timing (etc) and you'll get crappier mileage.

That's my short and skinny on it.

[rockfangd]

very true. My best friend and I both had 96 Devilles (still have mine) and I always run premium and he ran whatever he could afford, we both love the throttle but his had octane tick and mine is silent. His burned through gas and bucked a lot. Mine is good. Also his smoked alot where as mine barely smokes. his had 120000 mine has 196000