Reg versus Premium Fuel experiament in 09 PT Cruiser

I have pretty much gotten a decent feel for the gas mileage to expect
from my PT. The last three tanks averaged about 23 mpg. So when I
filled up yesterday I put premium in it instead of regular. It's too
early for a definitive answer but so far it looks like it's down 2 mpg
over what I'd been getting. About what I expected but I thought I'd
test it out.

 

I don't know for sure, but there are those that would say that you have
to give your PCM time to adjust to the different fuel to make a
meaningful mileage measurement.

 

It should be down a little. Premium has less energy per unit volume.

 

That used to be true (say 30 years ago), but these days it is not
ture.

Ed

 

I had a Neon RT. I did an extensive milage test early on. I did ten
tankfuls of regular, then ten of premium, figuring the variance of each
set. The milage with premium was down a little, but less than one mpg.
However, the variance in each set of runs was over 1.5 mpg, so I had
to conclude it made no difference.

I think the Neon engine was very similar to that in the PT (though mine
had the DOHC heads).

 

If higher octane ratings are achieved through oxygenates it certainly
will be lower because those high octane oxygenates have less
energy/volume. I think it is highly unlikely that higher octane ratings
would be achieved through aromatics these days for fuels one can buy at
regular gas station.

http://www.epa.gov/oms/rfgecon.htm
http://books.google.com/books?id=J_...onepage&q=energy content of gasolines&f=false

 

High Octane has the same energy. It has a higher OCTANE and is wasted or
may not be burned as completly in a low compression motor or with
retarded or less advance in the timing of ignition. It burns slower and
does not detonate under heat of compression as easily as regular.
Fuel that uses more ethanol to increase octane has less energy. Regular
fuel with ethanol has less energy.
A 12 to 1 compression or even 14 to 1 compression motor burning 105
octane or higher will get better mileage and torque if the ignition
curve etc are right.
Just like diesel the motor has to be built for the stress.
What we have now and for a long time is junk engines designed to be
built as cheaply as possible and to run on junk fuel as per EPA or
California really. The electronics are good at getting the most from
junk. Just imagine what great engine structure and electronics would do
with great fuel.

 

That's what I was thinking. I wonder how much alcohol they are
allowed to put in basic gasoline. Maybe the main difference between
regular and premium these days is the amount of alcohol they put in
it.

 

I don't understand you claims of "junk" engines. Today's engines are
far better in pretty much every way then everything that came before
them including durability. That's a general statement, there will
always be a few bad designs. Up until the mid/late sixties, engines
were so weak that it was common for them to need valve jobs before
100K and for many of them they needed both rings and valves before
that point. There used to be a thriving industry doing ring and valve
jobs there was such a demand for it.

 

My preliminary assessment is that it's down at least 2 mpg and
possibly as much as 3 or 4.

 

In our town, they can put up to 10% ethanol in the gas. I think it's
some kind of scam the state is taking part in but that's the brakes.
There is a slight drop in gas mileage but the good news is that I can
use the lowest grade of gas in my cars without knocking. Previously, the
cars had to use mid-grade.

 

They also finally figured out how to and/or decided to make CV joint
boots that could generally last the life of the car. They had to
replace those recurring multi-hundred $$ maintenance needs with
something else. That's when some genius said "Hey! I've got it! Let's
start driving the cams with timing belts in almost every engine, *AND*
let's bury the water pump inside the engine and have it be driven by the
timing belt! And to really mess up a few people's bank accounts, let's
make those same engines with the cams driven by high-tech rubber bands
to be interference!!".

 

Remember the Hemi of the late 60s, not the mid sixties. It put out an
honest 800 hp and 860 ft lbs according to modern testing a year or so ago.
They came apart because that much power and trying to rev past 8000 rpm.
If you kept it at 7000 or below everytime it stayed together. However
the head block gasket would seep a little bit of oil, if constantly
stressed.
Name me one engine that puts out that torque that you can afford. I've
got one of the modern high hp jobs. It revs like crazy but hasn't got
any torque. Next time you get a chance ride in a 70 442 w 410 gears, or
a Hemi Cuda properly tuned. A 429 Cobra Jet or a 428 for that Matter, or
a high winding 427 or a bunch more.
The new engines don't come apart becaause they don't put out power that
will break them. you 3.3 mph per second regulated electronic throttle is
a wuse. A hemi with modern developments could probably push 900 hp.
Street Rod Standards are now in the 1000 hp range. Try that with a
Mercedes engine short of 6.3 twin turbo. None of them will survive.
The reason the don't run 186 mph or above is rear gearing and no
overdrives in the gearbox. A 440 or hemi and a number of others would do
155 at 8000 but don't expect it to live.
Ride in a 427 Vette and wish it had the gearing etc box of the new
Vette. The technology is far more developed today but it is not applied
but who "needs" a 250 mph 900-1000 hp Hemi.
The new Hemi is more a Polsphere head It has an unfinished area to hold
heat and twin plugs to burn junk fuel.

 

But that has nothing to with the engine itself. To claim that burning
rings and valves is evidence of a "weak" engine is silly. That
definition would mean the weakest engines are the ones used in dragsters
and race cars.

Take a hundred of what you think are the best built car engines today
and install a breaker-point ignition and a carburetor on them and you'll
find out the rings and valves don't hold up as well as the cars that
were designed with those old fuel and ignition systems.

The point that I think was being made was that toady's manufacturers
and oil companies are delivering cheaper quality to the consumer, but
the electronics used today more than compensate for that.

-jim

 

That is a lot! How many tankfuls and what is the variance of the test?

 

http://www.chevron.com/products/our...technical_safety_bulletins/ogfe_enrgycon.aspx

From
http://www.chevron.com/products/ourfuels/prodserv/fuels/documents/69083_MotorGas_Tech Review.pdf :

"Conventional fuels always have varied in heating value. One cause is
the formulation differences among batches and among refiners. A survey
of 1990-1991 conventional gasolines found that the heating value of
summer gasolines varied over an 8 percent range. Heating value also
varies by grade and by season. On average, the heating value of
premium-grade gasoline is about 0.7 percent higher than regular grade
because premium grade, in general, contains more aromatic
hydrocarbons, the class of hydrocarbons with the highest densities.
The heating value of winter gasoline is about 1.5 percent lower than
summer gasoline because winter gasoline contains more volatile, less
dense hydrocarbons.

"Oxygenated gasolines (see page 53) have lower heating values because
the heating values of the oxygenate components are lower than those of
the hydrocarbons they displace. The percentage decrease in heating
value is close to the mass percent oxygen in the gasoline. For
example, in keeping with federal regulations, gasoline in carbon
monoxide nonattainment areas in the U.S. is oxygenated to a minimum of
2.7 mass percent oxygen during four or five winter months. The heating
value of the oxygenated product is about 2.7 mass percent lower than
that of conventional gasoline. In addition, federal RFG and California
Phase 3 RFG in federal RFG areas are typically oxygenated year-round
to an average oxygen content of about 2 mass percent. The resulting
heating values are about 2 percent lower than that of conventional
gasoline. California Phase 3 RFG also has limits on distillation
temperatures and aromatics content, which has the secondary effect of
lowering the density of the fuel. These limits reduce heating value by
about another 1 percent.

"The gasolines that produced the results displayed in Figure 1.3 were
specially formulated to span a wide range of compositions. The
compositional variations were much greater than those separating
conventional and reformulated commercial gasolines. Thus, the results
provide solid evidence that RFG does not exert an unusual effect on
fuel economy. Individual drivers have reported decreases of 10
percent, 15 percent, and even 20 percent in fuel economy when they
began using RFG. Not surprisingly, many of the claims are anecdotal.
Most drivers do not keep continuous fuel-economy records, so they don't
have a meaningful fuel-economy baseline for the gasoline they
previously used. Even with a baseline, a fuel-economy value based on
the consumption of a single tank of gasoline can
be misleading. Drivers interested in fuel economy should average
results over several tanks of gasoline or, better yet, over several
months of driving."

From http://www.api.org/aboutoilgas/gasoline/gasoline-octane.cfm :

"Gasoline with a higher heating value (energy content) provides better
fuel economy. Traditionally, premium gasoline has had a slightly
higher heating value than regular, and, thus, provides slightly better
fuel economy, but it is difficult to detect in normal driving. There
can be even larger differences in heating value between batches of
gasoline from the same refinery, between summer and winter volatility
classes, or between brands of gasoline from different refineries
because of compositional differences. The differences are small and
there is no practical way for the consumer to identify gasoline with a
higher-than-average heating value."

 

I saw some of that on my own. it's just longer ways of saying the same
thing and some additional detail. RFG has been around for 14 years now.
Even when I've been out in the middle of no where, well outside the RFG
mandated areas ( http://www.epa.gov/otaq/rfg/whereyoulive.htm ) the
fuels have at the very least contained ethanol if not fully RFG
compliant. Do any refineries make anything else now? (I thought ethanol
was a federal requirement anyway)

Once adding that stuff the easier way to higher octane is just putting
in more of it.

 

Now you're just being silly. Talking about 800 hp engines the
comprised 0.002% of the market is meaningless. In the 60's your
primary engines were the Chevy and ford 6's and small block v8s and
similar in the upscale cars like Buick, Lincoln, etc. Not only the
engines but the cars themselves were often worn out within 10
years/100K miles. If you want to talk about power, consider that back
in the day a typical 6.6+ Liter muscle car might do 0-60 in 6.6
seconds, I forget their quarter mile numbers. My 99 GT with 4.6L
motor can do the same 6.6 and quarter, more or less. And instead of
getting 13 mpg I can get 18 mpg or better. Heck, people with new
Corvettes that will blow the doors off the Corvettes from back in the
day, have reported 30 mpg on trips. You are living on some other
planet if you believe what you are writing.

 

I suppose we could split hairs over the quality of the lock washers
too. It is what it is and is what it was. Today's clearances are
much tighter, the engines are cleaner burning, etc. Sure, if you want
to take a complete system (today's engines) that was designed for
today's technology, and remove part of it and substitute parts it was
never designed to use, sure, you can make it worse. Next you be
singing the praises of wooden wagon wheels over modern tires because
the wooden ones never blew out from being run low on air.

 

Just a few. But keep in mind that unlike having to run several full
tanks over similar but not identical courses, and then calculate the
overall mpg, I can get immediate readout from the computer in the car.
That's mainly what I'm looking at. I can run on the exact same street
at the exact same speed, resetting the computer at the start, and
immediately get the mpg results. Ditto on my "high speed" daily
commute. So it was immediately apparent that the mpg was down just
about as soon as I left the gas station after filling up. It's been
the same every day, whatever I was getting as "instant" mpg with
regular gas is down about 2 mpg now that it's burning premium. When
this tank runs out and I go back to regular if it goes back up it will
be just as immediately obvious. I'm looking at the trend, not
particularly an exact number.