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2014 LT program car, Pull Me Over Red, 1.4T Auto
14,330 Posts
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.
I used to fuel up at a northern IL Marathon station as it had the best price for 87 octane (old 360 BB ford) and I used about 2 tanks a week. I noticed that I was getting lousy mileage as compared to when I fueled up in WI. At the time, IL dropped the fuel tax so gas in IL was then cheaper. Needless to say I no longer purchase from Marathon.

Brace yourself, this could get boring.

It may take a few tanks to get the full benefits of a highly knock resistant fuel like 93. The car has knock sensors and will "pull" or retard the timing on the engine if it senses knock (aka pinging or predetonation). Knock happens when you put the air/fuel mix in a condition where it spontaneously combusts before the spark plug gets a chance to ignite it at the optimal time. When the air/fuel detonates too early, it can harm the engine. The cruze has timing tables for fuel as low as 87 octane so you can safely run cheap gas but there are side effects. The 1.4L engine in the Cruze is turbo charged so the air pressure going into the cylinder is higher than naturally aspirated cars. When you increase pressure of a gas, the temperature increases. Some of that extra heat is removed by the intercooler. But since the intercooler is sandwiched in between the coolant radiator and the A/C radiator, it will often heat soak in the summer, in traffic, or with A/C use. That's when the air intake temps skyrocket and cause knock, so the computer retards timing to protect itself which results in decreased power. Not a huge deal, but since the Cruze is heavy, and doesn't have a lot of power to begin with, now it has to use more fuel hence the decreased economy. Depending on how you drive, you may not notice it. But if you have a lead foot, you'll lose a pretty significant amount of MPGs running 87.

You can kind of get away with running 89 or 87 in the winter because the intake temps stay low. When air is cold, it's dense and more potent. Usually that means you can get more power, but the Cruze is torque limited so it uses the boost levels to control how much torque it makes. Since it can easily achieve the 148 ft-lbs in the winter with that delicious dense cold air, it doesn't need as much boost so the pressure is lower, which means the temps are lower, and since the winter air is already a lot colder, the air fuel/mix is a lot less likely to pre-detonate so the computer doesn't need to retard the timing. You'll still get less fuel economy in the winter no matter which grade you run because they have to blend in extra chemicals to keep the fuel from freezing, and it also takes the car a lot longer to reach operating temperature so it runs rich more often in winter.

Hope this helps.

That was a mouthful! Pretty interesting though.
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