A friend of mine has begun posting photos of gas pump digital displays after each fillup, which costs her an astonishing $70-$80 now. I noticed that she’s been consistently buying the middle grade of unleaded gasoline, labeled ‘Plus’ at the Chevrons she frequents. As someone who invariably buys the cheapest gas possible, I started wondering if the higher grade was strictly necessary.
Here’s what Consumer Reports has to say on the subject:
Don’t use premium fuel if you don’t have to. If your car specifies regular fuel, don’t buy premium under the mistaken belief that your engine will run better. The only difference you’ll see is about 20 cents more per gallon. Most cars are designed to run just fine on regular gasoline. Even many cars for which premium is recommended will run well on regular. We have found that the differences are imperceptible during normal driving. Check your owner’s manual to find out if your engine really requires premium or if you can run on other grades.
Next I looked up the owner’s manual for my friend’s late-model Ford sedan:
Your vehicle is designed to use “Regular” unleaded gasoline with pump (R+M)/2 octane rating of 87. We do not recommend the use of gasolines labeled as “Regular” that are sold with octane ratings of 86 or lower in high altitude areas.
If you are experiencing starting, rough idle or hesitation driveability problems, try a different brand of unleaded gasoline. “Premium” unleaded gasoline is not recommended for vehicles designed to use “Regular” unleaded gasoline because it may cause these problems to become more pronounced.
One more web search confirmed that Chevron “Regular” gasoline is 87 octane, and “Plus” is 89. In my friend’s most recent gas pump photo, Plus was listed at $4.639 per gallon, Regular at $4.439. That’s 20 cents per gallon she can save, just by switching gas grades.
If you’re currently buying a higher gas grade, double-check your owners’ manual to make sure it’s recommended for your particular vehicle. And even if it is, you might consider trying 87 octane gas anyway, since as CR says, “the differences are imperceptible during normal driving.” The savings will add up!
(Photo by glenn.batuyong.)
Gasoline prices are on the mind of nearly every American right now. Here in Seattle, where gas is currently climbing past the $4.50 mark, we like our hybrid cars. A lot.
But Seattle had an environmentally ‘green’ culture long before the recent spike in gas prices, which suggests that a lot of those hybrids are being purchased by people who already had reasonably fuel-efficient cars.
Which is fine, but upgrading your existing 30 mpg vehicle to a 50 mpg hybrid won’t help nearly as much as upgrading from 15 mpg to 25 mpg.
Wait, what? Shouldn’t an increase of twenty miles per gallon be twice as good as an increase of ten miles per gallon?
Actually, no — in this case, it’s only half as good.
Turns out that our intuitive math is all wrong, thanks to the ‘miles per gallon illusion’. As explained last week on NPR’s All Things Considered, the number that really matters is ‘gallons per mile’.
Like this: a 15 mpg minivan uses .0667 (1/15) gallons per mile — or to make the numbers a bit easier, 6.67 gallons per 100 miles. A 25 mpg station wagon needs 4 gallons to go 100 miles. Trade the minivan for the wagon, and you’re saving 2.67 gallons per 100 miles. (That’s worth about $12 in Seattle right now.)
Now, a 30mpg sedan uses 3.33 gallons per 100 miles, compared to 2 gallons per 100 miles from a 50mpg hybrid. That’s a savings of 1.33 gallons per 100 miles (currently $6).
Or, only half the improvement of the 15-to-25 mpg upgrade.
The way cars are advertised in the States (the rest of the world, apparently, gets it right) leads people to make the wrong decisions about which cars to upgrade. A 3 mpg improvement hardly seems worth the bother … and if you’re already getting 30 mpg, it’s likely not. If you’re going from 12 mpg to 15 mpg, though, the difference is a lot bigger than you probably think.
I confess that I am periodically tempted to trade our 1999 Civic (rated as a respectable 24 mpg in-city, but in practice we get over 30 mpg) for a shiny new (or at least new-ish) hybrid. But even though we could literally cut our gas bill in half, it wouldn’t come close to making up for the roughly $16K more we’d have to spend to trade up to, say, a 2006 Prius. Gas will need to be a lot more expensive for that math to work out.
Update 14-Jul-08: Rick Larrick of Duke University offers a more thorough mathematical explanation of the problem.
(Photo by Casey Hamilton.)
