different gas, different gas mileage

I've always liked chevron gas because it has techroline, which is one
of the best fuel detergents. But I've noticed lately that when I buy
Chevron my 2009 PT seems to get about 2 - 3 mpg worse gas mileage. My
other typical fill up is some "FastGas" type place. This change has
happened often enough that I'm pretty sure it's not completely my
imagination. Anyone else noticed such a change from one brand to
another? On the FastGas I usually get 24.5 on my typical driving
cycle, 70% commute, on the Chevron it drops down to about 22.

 

Brands have different additives, but nothing that should affect
gas mileage given equal octane. Most likely it's just plecebo effect.

 

Amount of alcohol added, seasonal blend formulations and accuracy of the
blend, quality of gas as far as moisture/water due to condensation that
collects in the tanks, particularly during th winter can be a factor.

 

10% ethanol out here and that's not a seasonal thing.

local techs recommend a small amount of amsoil 2 stroke in your gas tank but
a very small amount, about 1 ounce per 10 gallons i think but i am checking
on that now.

 

Are these by any chance techs who make a large profit on replacing
catalytic converters?
--scott

 

"Ah, you used a bit too much..."

 

lol really


Well.... maybe it's no different than putting Marvels Mystery Oil in
the fuel???

 

Hard to get accurate mpg without controlled highway driving.
Catching more red lights, more idling, and a few pedals to the metal
could account for that difference.
You need multiple tanks of the same stuff, then multiple tanks of the
other, and careful attention to driving style.
If there's a cold snap during one brand test but not the other, toss
everything out, and start again.
You might find a difference.
But do you really want to do that?

--Vic

 

While I agree that different brands likely will have SOME difference in
energy content and milage, that seems like a lot.

You need to do a good milage test and compile statistics.

You need to do about ten samples to get a real valid test, so this is
ten tankfuls each. Then figure the milage individually for each of the
ten tankfuls and use one of those "statistics" calculators. You need to
determine the Probable Error of each set of tests.

A number of years ago I bought a Dodge Neon that would run on either
regular or premium but they recommended premium and said I would get
better milage on premium.

I ran ten tankfuls of each. The tests said I got about 0.3 mpg better
on regular. But... the probable error on the testing calc'd out at 0.5
mpg. It is very hard to measure mpg differences of about one mpg.

But, two to three ought to show up well.

 

As I've posted before, my 2001 PT gets terrible milage.
Here in Western PA and Eastern Ohio there's a huge supermarket chain,
Giant Eagle.
They have GetGo gas stations. For every $50 you spend at the market,
you get 10¢
off a gallon of gas. The only time I use GetGo gas is when I have a
free tank coming.
My cruiser on BB, Sunoco or Shell averages 16-17 mpg. My trips never
change. I'm
usually going to the same places the same number of times between fill
ups.
On the GetGo gas, I'm lucky if I come close to 13-14 mpg.

 

What have you done about it? Any codes in the ECM? Checked for vacuum
leaks? Changed plugs, cap and rotor? Checked fuel pressure? Or just
ignored it?
--scott

 

I get better than that with my 41 Windsor! 245.5 flathead 6.
I had two PTs: a sedan and a convertible. Both got terrible mileage, the
convertible with the 180hp turbo, got around 17-22 max. The sedan, with the
base engine would get around 19-26. This is Florida with flat roads
everywhere.

 

The best I've ever done on my wife's 2005 PT (automatic) was 27.5 on the
highway. More typical is 24-25, and around town is 20 to 21. I don't
consider that particularly good since her 3.5L Vision TSi that
out-weighed the PT by a few hundred pounds and out-powered it by almost
100 horsepower got even better mileage (30 highway when it was in its
prime). But what I really can't understand why your 2001 does so badly.
I know other owners of early PTs which were similar to yours, though.

 

Maybe it's different where you are, but here in VA, the decals on the
pumps say something to the effect "May [ < key word] contain up to [ <
more key words] 10% ethanol", so to me it is a real unknown, and who
knows *what* determines from one batch to the next what the exact
content is?

--
Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

(Scott Dorsey) wrote in

Notice "Rob" hasn't got back to us about the results of his "checking"?

 

I always record each and every fillup, writing down the odometer reading,
how much went into the tank, and even the date and price.

Over 19 years, with an average of almost 18,000 miles per year, I have yet
to notice /any/ discernible difference in mileage from one brand to
another.

Because accurate results require very long-term measuring over many
fillups, I run into seasonal temperature variation, which is a confounding
factor.

However, there /is/ considerable difference in mileage from summer to
winter and back again. This difference appears to be unrelated to gasoline
brand.

There is also considerable difference in mileage when taking a single
fillup against the others. I've seen as much as 15% variance in mileage
between individual fillups. The variance is erased when many fillups are
included in the calculation. This is true even when batches of fillups
overlap.

I used to think I had seen an approximately 2% drop in mileage between 87-
octane and 91-octane, but now I'm not so sure. My test periods extend over
two or more seasons, so that 2% could easily be explained by temperature
variation.

These are just my very careful observations. Take them as you will.

 

Clarification: the word "however" should not be in this paragraph. I
ngelected to excise it while rearranging my previous post.

 

that's because some of us have a job.......i cant sit on the web and surf
all day

 

yeah same thing down here.......up to 10%.

 

But you said you were "checking on that now". So you're admitting you were
fibbing?