MPG difference with different gas?

I used to think that there could not possibly be any significant difference
in MPG from one gas brand to another. However I now do seem to be noticing
a difference.
When I use 76 Gasoline from my local gas station in Milpitas California I
seem to get:

20.5 MPG from my ’98 4x4 Nissan Frontier and 32.0 MPG from my ’88 Mazda
323 and 32.5 MPG from my ’89 Honda CRX

On the other hand when I use Shell gas from my local gas station, I get:
24.0 MPG from my ’98 4x4 Nissan Frontier and 37.0 MPG from my ’88 Mazda
323 and 38.0 MPG from my ’89 Honda CRX

That seems to be a 15-17% more with the Shell gas!!
I’m having a hard time believing it but I’ve already done the experiment
twice with each car and the results are consistent.
Can this be possible?

On Mon, 24 Apr 2006 14:48:12 -0400, "ThomasE" >
wrote:

> That seems to be a 15-17% more with the Shell gas!!


This usually should not make so much difference, but:

Is either 10% ethanol?
Is either a winter formulation?

Even though they're supposedly inspected, there COULD be a small
metering defficiency. With gas so valuable on a per gallon basis, it
wouldn't surprise me if there were some tinkering involved ...
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There can be a difference, but your results seem too dramatic.

MTBE additive reduces mpg by about 3% at the maximum concentration used
in metropolitan areas. (about 11% as I recall.)

Ethanol at 10% (the maximum allowed) reduces mpg by an *additional* 3%.

So, going from pure gasoline to ethanol would result in some 6%
reduction in mpg.

If your lower-mileage gas pump is off a few percent (call your state
weights and measures department), plus 6% loss from additives (you'd
probably have to cross county lines for this to happen), plus a few
percent change due to different branding or volatility..... I guess it
could happen.

ThomasE wrote:
> I used to think that there could not possibly be any significant difference
> in MPG from one gas brand to another. However I now do seem to be noticing
> a difference.
> When I use 76 Gasoline from my local gas station in Milpitas California I
> seem to get:
>
> 20.5 MPG from my ’98 4x4 Nissan Frontier and 32.0 MPG from my ’88 Mazda
> 323 and 32.5 MPG from my ’89 Honda CRX
>
> On the other hand when I use Shell gas from my local gas station, I get:
> 24.0 MPG from my ’98 4x4 Nissan Frontier and 37.0 MPG from my ’88 Mazda
> 323 and 38.0 MPG from my ’89 Honda CRX
>
> That seems to be a 15-17% more with the Shell gas!!
> I’m having a hard time believing it but I’ve already done the experiment
> twice with each car and the results are consistent.
> Can this be possible?
>
>
it's possible, but 17% is a little extreme. 10% is much more within a
usual range. keep the experiment running and see how it averages out
over a longer period, then report back.

OK, I’ll keep logging the MPGs a few more times to see if the results
remain consistent. Actually, when I first noticed the difference on the
Nissan I thought that perhaps the engine was getting a bit out of tune, so
that is when I repeated the experiment with my other two cars and got
similar results.
My only other similar experience was a few years ago when we had an ARCO
station in the neighborhood. The ARCO gas station was using 10% Ethanol in
the winter months and I had then noticed a small decrease in MPG, around
5-6%, with the ARCO gas compared to Shell using my ’88 Mazda 323. I had
also noticed that the engine was running a bit rougher and had a little
less power with the ARCO(ethanol) gas, but in any case the differences
seemed small. I started preferring gas from other gas stations and since
then I have only occasionally checked gas mileage until now I noticed this
bigger difference.
I sometimes check MPG on long trips (ie. Primarily highway driving) as an
indication of engine health.

Thats strange, a car mechanic once told me that amongst the top tier
gas companies, 76 is supposed to be the best for Hondas?

"ThomasE" > wrote in message
lkaboutautos.com...
>I used to think that there could not possibly be any significant difference
> in MPG from one gas brand to another. However I now do seem to be noticing
> a difference.
> When I use 76 Gasoline from my local gas station in Milpitas California I
> seem to get:
>
> 20.5 MPG from my '98 4x4 Nissan Frontier and 32.0 MPG from my '88 Mazda
> 323 and 32.5 MPG from my '89 Honda CRX
>
> On the other hand when I use Shell gas from my local gas station, I get:
> 24.0 MPG from my '98 4x4 Nissan Frontier and 37.0 MPG from my '88 Mazda
> 323 and 38.0 MPG from my '89 Honda CRX
>
> That seems to be a 15-17% more with the Shell gas!!
> I'm having a hard time believing it but I've already done the experiment
> twice with each car and the results are consistent.
> Can this be possible?


Yes but...

You need to log a year with one brand, then a year with another, so as to
iron out any statistical oddities.

--
The DervMan
www.dervman.com

On Mon, 24 Apr 2006 14:48:12 -0400, "ThomasE" >
wrote:

>I used to think that there could not possibly be any significant difference
>in MPG from one gas brand to another. However I now do seem to be noticing
>a difference.
>When I use 76 Gasoline from my local gas station in Milpitas California I
>seem to get:
>
>20.5 MPG from my ’98 4x4 Nissan Frontier and 32.0 MPG from my ’88 Mazda
>323 and 32.5 MPG from my ’89 Honda CRX
>
>On the other hand when I use Shell gas from my local gas station, I get:
>24.0 MPG from my ’98 4x4 Nissan Frontier and 37.0 MPG from my ’88 Mazda
>323 and 38.0 MPG from my ’89 Honda CRX
>
>That seems to be a 15-17% more with the Shell gas!!
>I’m having a hard time believing it but I’ve already done the experiment
>twice with each car and the results are consistent.
>Can this be possible?
>

It's always possible with modern automobiles with computer operated
spark advance. If you buy gasoline with an octane lower than what the
engine requires, the computer will retard the spark thereby reducing
power and gasoline mileage. I can definitely see that when going from
87 octane to 85 octane in my Jeep. I usually stay away from 3-pump
stations (85, 88, 92 octane) for that reason. At those stations I
have to buy the middle grade which is much more expensive than the
regular at a 2-pump station (87, 92 octane.) Of course this varies by
location and altitude. I would trust the octane rating at a Shell
station a lot more than a neighborhood generic station. You may be
getting 85 when you think you are getting 87.

You may be
> getting 85 when you think you are getting 87.

That's a great point. But it is also sometimes possible that you're
getting a higher octane than you may think. A tanker truck may be
emptied into a "regular" storage tank at the pump, rather than haul the
load all the way back to the distribution terminal.

On 25 Apr 2006 09:48:34 -0700, wrote:

> You may be
>> getting 85 when you think you are getting 87.
>
>That's a great point. But it is also sometimes possible that you're
>getting a higher octane than you may think. A tanker truck may be
>emptied into a "regular" storage tank at the pump, rather than haul the
>load all the way back to the distribution terminal.

Well, I think each tank truck must have a million-dollars in fuel on
board, so they are probably very careful where they put it. :-)

I'm surprised they aren't being escorted with armored cars.