i use a shell credit card for fuel purchases - it carries a 5% discount on all shell gas plus shell is a top tier fuel provider which has something to do with fuel additives if i recall correctly

 

I just completed my third tank of 87 octane and again got in the high 16s (MPGS) versus the low 17s with 90 octane. I filled my LS with 93 octane today and will run a few tankfuls to see what I get with 93. I'll keep you all (or, as some here in Pittsburgh say... "yinz") posted.

 

I have just done the math. If using a lower grade of gas means getting ONE Mile Per Gal less--it's not worth it. I assumed 19.5 mpg on premium @ 4.089 vs. 18.5 mpg on Mid range @ 3.939--driving 13,000 miles per year. I also calculated this on my wife's RX350. She drives 10,000 miles per year and we have often tried different grades of gas and kept excel spreadsheets on the results. (her mpg is 17.51 on Regular, 19.49 on Mid-range, 20.55 on Premium)The better gas pays for itself in miles per gallon.

 

Interesting. You may be right. The mileage difference between 90 octane (mixing 87 and 93) and 87 octane appears to be about half a mile per gallon (low 17s versus high 16s). For that I save about 30 to 40 cents per gallon. Let's say merely 30 cents. So to go 16.75 miles would cost $3.88 at today's prices or .232 cents/mile for 87 octane.

To go 17.25 miles on 90 octane $4.03 would equal cost .234 cents/mile. Almost exactly the same. It will be interesting to see what mileage I get with 93 octane after a few tankfuls. I'll report here when I've done so. Of course at some stations premium is even more than 30 cents above regular. I guess as the price of gas has exploded, the difference between regular and premium has contracted (relative to each other).

So maybe I am being pennywise and pound foolish. We'll see. Stay tuned.

 

Not to sound arrogant, but who cares about gas mileage on a $80K car? Even at $5 per gallon, gas is still very cheap here in US. There are only 3 or 4 countries where the gas is cheaper than here. Our problem is not gas prices. Our problem is too many people living beyond their means.

 

Might want to check your math again ... if you mix 87 and 93, then your savings is HALF the difference. That difference in this area (and most I've traveled in lately) is usually 15 cents per grade, or 30 cents total as between 87 octane Regular and 93 octane Premium.

So, half of 30 cents is 15 cents per gallon saved. As in, 10 gallons at $3.80 + 10 gallons at $4.10 = 20 gallons at $3.95.

.
.

 

Oops. Thanks!

 

On the one hand I hear you. On the other hand, it's just my nature to prevent wasting money. That's how I got to Lexus status in the first place!

 

I hear you. But between 87 and 92 octane gas the difference here is $8.40 per tank. This difference is less than what a beer costs at a baseball game here. I think it's all a matter of perception.

 

So what was the final 3 tank premium average? I'd bet its the best of all the tests.

I have this fight with everyone, from friends to family. Even my friend, in his Mini, got better MPG when he stuck to premium (which it requires.) My mom is really old fashioned. . .brand new Cayenne, and she's putting 89 in it. Why? To save $0.20?

Its all pump psychology. People will wait in line for several minutes to get $1.99 gas when they can get $2.04 across the street. You'll eat up the savings in 5 minutes of idling.

 

I'd like to hear the results also. Interesting thread!

 

I finished the study in the spring but I guess I forgot to post it. I don't have the numbers, but I concluded at $4/gallon it paid to buy the highest octane. But at much lower prices...like now at $2.50...mixing the gas is cheapest. Because premium is about 30 cents higher at both levels.

I am sorry my answer is is fairly vague. I did all the math but did not save it and I guess I forgot to post it.

 

Just completed a round trip drive to Vegas and I had 605 miles showing since filling up with another 50 on the remaining range read out when we finally stopped for gas nearing home. Amazing.

It took 20.8 gallons to fill it so there were 1.3 gallons remaining and although that may be waiting a bit long to fill up, I and my passengers were very impressed. Speeds varied thru three states from 55 to 75 mph.


Pat

 

Just completed a round trip drive to Vegas and I had 605 miles showing since filling up with another 50 on the remaining range read out ....

Yea, but when you consider how much you lost at the tables, you only got 2 mpg!

 

I only use Top Tier gasolines in my cars.

http://www.toptiergas.com/retailers.html

They have more, sometimes substantially more, detergent packages in their fuels. This keeps injectors and combustion chambers clean for maximum LONG term efficiency. If you have a short term lease then perhaps squeezing a few cents here and there makes sense. I drive my cars till they are no longer economically feasible to repair. Am considering letting the Infinity G35 go with 156k miles. Chevy van has 220k.

If you look around the cost of top tier gas is the same.
And if an engine is retarding the ignition to burn regular you ARE loosing performance whether you can perceive it or not.
I too am a tightwad; have only bought 2 new cars in my life and both were for the wife. Fuel is not the place to pinch pennies IMO.