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410 Posts
Discussion Starter · #1 · (Edited)
So I was thinking,
Premium fuel is pretty high in price.
I usually fuel regular.
And as some have noticed, the Cruze doesn't do well with regular when the temps exceed 100F.

I was thinking in my 13Gal fuel tank, to add 2 gallon of E85 fuel for every 11 gal of Regular fuel.
It should be exactly the same price as a tank of regular, but it'll result in E14 (higher knock resistance than regular, pretty similar to Premium fuel).

The price of a full 13GAL tank here locally at $2.69/gal is exactly $35.
This would be the same as a tank of Regular + E85, as E85 is sold here at the same price as regular (in your area too?).
If I would fill up with premium, at $3.09/gal, I would pay $40 for a tank.

$5 extra for a tank might seem silly, especially since Shell premium fuel usually has 5% better MPG than Shell regular (which brings the total price closer to $3 surplus per tank).

And I'm only expecting that 2 gal of E85 is enough to make the fuel similar to Hi-Octane fuel in terms of knock resistance, which is more of a guess than an actual measurment.
Open for discussion on more technical data on E85 octane rating!

So, if I would do 500 miles on a tank of regular fuel (13GAL),
I would do 525 miles on a tank of Premium (Hi Oct) fuel under the same conditions.

On the other hand, E85 is about 30% less efficient than regular fuel (according to some sources, more proof needed) , so in order to go just as far as 13 gallons of regular fuel, I would do:
11 gallons of regular (500/13*11) + 2 gallons of E85 (500/13*2*0.6), and that gives me 470 miles.

Now we can compare the range of all tanks (regular, Regular + E85, and premium), with the price paid:

Reg: 14.28 miles per dollar.
Prem: 13.12 miles per dollar.
Reg+E85: 13.42 miles per dollar.

When we look at the above numbers, and use Regular as our reference (base), and convert the miles/dollars to percentage, we get:
Reg: 100%
Prem: 92%
Reg+E85: 94%

Our current numbers indicate going Premium is the least economical, and going regular is the most.
And adding 2 gal of E85 in an 11GAL regular tank, will result in a 6% loss, however, there will be less heat soak/knock losses.

Using regular + E85 over Premium would make sense, if Premium gasoline prices are 10-15% (or higher) priced than regular fuel.
Otherwise (premium fuel prices are <10% surplus over regular), use premium gasoline.

Most people wouldn't go through the trouble of mixing E85 with regular, if your local pump doesn't serve E85; but if you have both fuels at the same pump near your home, why not?

Open for discussion!

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410 Posts
Discussion Starter · #3 ·
Another thing they've noted, was that the E85 fuel, has more water in the fuel, the nature of Ethanol, to attract water, which causes the engine to cool down more, and could result in better fuel efficiency.

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410 Posts
Discussion Starter · #4 ·
From the manual courtesy of Nick!
"However, E85 (85% ethanol) and
other fuels containing more than
15% ethanol must not be used in
vehicles that were not designed
for those fuels."

Why not try a gallon of Sunoco Racing fuel or "Sunoco 100"

Sunoco SS 100 is an unleaded high octane gasoline that is street-legal in California. Its 100 octane rating will allow increased boost levels in supercharged or turbocharged applications compared to premium pump gas. Sunoco SS 100 can be used in high performance vehicles both old and new.
Mainly because of price, and we're not racing the engine, just trying to prevent knock or delayed ignition due to hot outside temps.
Racing fuel with 100oct would be nice to add to regular fuel, if they were cheaper than Hi-Oct fuels (usually 92/93)

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410 Posts
Discussion Starter · #8 ·
My personal recommendation would be to fuel the car with 91+ octane.

As you've noticed the Cruze computers are sensitive to knock and will retard engine timing to protect itself if it senses pre-detonation. Knock is caused by the fuel exploding too early in the cylinder due to high temperatures, and high pressures. Since the Cruze is turbo charged, it's a check mark for high pressure. The intake temperatures vary wildly depending on conditions. But basically you're going to reach high temps at least a few times each tank of fuel. The exception is in winter when the temps are always cold.

I've toyed around with various grades of fuel and have settled on 93. I get better fuel economy with premium, which is almost enough to completely offset the price increase. Also, when I run 87 my car is very quick to pull timing and as a result it feels very under powered. Just feed it premium. It's not like it chugs gas. A car is generally your second biggest purchase, no sense in fooling around with mixing fuels it's not recommended to run just to save a few dollars. If you really want to save money on fuel, buy a 50cc scooter on craigslist, they get 110+ mpg and I wouldn't feel the least bit bad for filling it with 87 octane. Or bicycles I hear are an option for some people. Much cheaper.
I've noted that many premium blends, Shell, BP, use nitrogen based boosters, causing more violent combustion, and the engine to vibrate more, while E85 uses a much more slow burning, better suited for low revving cars like the Cruze.

I've always felt like my engine would wear quicker when I use hi octane fuels from BP and Shell, for this purpose.

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410 Posts
Discussion Starter · #13 ·
I don't think adding 2 gal of E85 fuel will cause any major damage to the engine, especially if you ride it off pretty frequently (fuel up at least once a week).
Regular gasoline already has UP TO 10% of corn juice in it.
And from my experience here in SoFlo, Marathon is closer to the 10%, while Shell is closer to 2%.

As long as the concentration is not too high, it shouldn't do too much damage.
What causes most damage, is water getting in the fuel tanks, 'drowning' the engine with non-combustible fluids, that work best on a hot engine.

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410 Posts
Discussion Starter · #19 · (Edited)
I can only compare it to my current Fiesta ST.
However, the Cruze should be under the same regulations.
They're made to be compatible with E15. On my Fiesta ST, there's a note "No fueling E20-85".
Strange. I probably could fuel diesel, or E100 and get away with it, 'legally' that is, because the sticker didn't mention not fueling anything above E85 nor diesel.
My experience with E fuels indicates that my ST is running better on a blend of 50% regular 87 octane, and 50% E15; resulting in ~E10-E12, with a 88 octane rating.
Anything higher (pure E15, E30,..) runs less efficient (lower MPG) and less power.

The hotter your engine runs, and the more knock it has, the higher you can tune your Ethanol levels.
If your engine runs very cool, on the stock turbo, there's no reason to believe it actually has more power on E15 or above, than below.
In fact, more than likely, the higher you go on ethanol levels, the lower your performance.
Unless you compensate by higher exterior temperatures, higher compression ratios, higher boost, or higher back pressure.

I think the only cars that benefit from E15 would be the 1st gen 2012+ models that are made to support E15 fuels, as they run considerably hotter than the Gen 2 models.
The 2011 Cruze (and especially the Eco models) don't have the proper fueling system to deal with higher ethanol fuels, and you probably could get away with E12 for a while.
But 93 octane is still a bit better.
I wouldn't do E15 in them, as they are made for E10 fuels and no more.

Running too much E85 in your fuel, and your car will run lean.
Some people on the Fiesta forum (especially those tuning their cars) have ran into piston problems due to lean burn, due to running too high ethanol levels (E50 and up).

If you had a dyno, you could do tests with what works best on your car.
But for my Fiesta, the butt dyno tells me the car accelerates best at 50% 87 octane, with 50% E15 fuel in a tank.
If your Cruze runs hotter, that ratio might be different.
You'd have to experiment.
And if you notice where the power starts to decrease (eg: E30 or E40), half that number, and that's roughly where your sweet spot is.
Eg: E40 starts accelerating slow, E20 is your sweet spot. Then try testing out E15 with E15+1 gal of E85.
I seriously wouldn't go over E20.
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