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Discussion Starter #1 (Edited)
For a car that uses very little gasoline, I would never have believed that something as simple as fueling the Volt would involve so many questions and so many discussions/disagreements. Below is a compendium of the various questions and answers we have seen on GM-Volt. Enjoy!

Executive Summary
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Here are the short answers to common questions. Below this post is another with more detailed answers containing citations, nuances, etc.

How do I open/access the gasoline tank's fill tube?
Use the button on the drivers door.

Should I top-off the tank after the nozzle clicks off?

No, unless you like dealer repair trips.

What kind of gasoline should I put in the Volt?
"Top Tier" detergent, 91 octane premium.

What is Top Tier gasoline?
A higher level of additives than regular.

Why does GM recommend premium gasoline?
Premium delivers higher MPG, engine cleaning, longer shelf life.

Is octane the same as BTU (energy content)? Does higher octane mean more energy?
No and no.

Premium does not have a higher BTU content, so why not use regular gasoline?
Regular produces lower MPG, potential long term damage.

What if I accidentally filled up with regular?

Your mileage will suffer. Add premium ASAP.

Can the Volt use E85 flex-fuel gasoline?
No.

Can the Volt's engine emulate the Atkinson cycle?
Maybe.

Will I save money using regular instead of premium?
No.

Does higher alcohol content affect mileage?
Yes, lower MPG.

Should I add fuel stabilizers like Sta-bil or other additives?
No.

What if I rarely use gasoline, won't the fuel eventually go bad regardless?
No, EMM will occur before then.

I'm getting a message that my engine needs to run, what's Engine Maintenance Mode (EMM)?
The engine hasn't run in 6 weeks, it's going to now.

How does the gasoline tank pressurization work?
The tank has a bladder.

Can I run the Volt with no gasoline in the tank?
In an emergency, yes.

Can I siphon the gasoline from my Volt's tank?
No.

When the dash switches to the gasoline icon, am I using gas?
No, but the Volt is now in a "use the ICE when needed" mode. The engine will come on at some point. Regen miles under this mode are counted as gas miles.

Why am I Using .5 Miles of Gas with a full battery?
It's complicated, but occurs when the battery is prevented from overcharging.
 

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Discussion Starter #2 (Edited)
Below are the more detailed answers.
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How do I open/access the gasoline tank's fill tube?
1. There is a button you press before refueling -- it is on the driver's door for MY 2014. It is on the driver's door above the charge door button for MY 2011-2013. Press to depressurize the tank (the tank is pressurized to help preserve the gas over long periods of no use, since you can drive for a month or more on electric under normal usage).
2. Then, the filler door on the rear passenger side can popped open by pushing on the filler door.
3. You can then unscrew the cap. The filler cap can't be unscrewed if the tank has not depressurized.

Should I top-off the tank after the nozzle clicks off?
No. Do not top-off (force-fill) the tank after the nozzle clicks off. This can flood the charcoal fume collector canister with gasoline, causing an error code and persistent gas smell in the rear of the car and requires a trip to the dealer for repairs/replacement.
See http://gm-volt.com/forum/showthread.php?15169-Ongoing-fuel-system-problem-since-new...now-worse-since-we-left-on-trip...&p=167544#post167544
and http://gm-volt.com/forum/showthread.php?11546-P0497-Error-Code-yet-no-CEL&p=118944#post118944
and http://gm-volt.com/forum/showthread.php?13918-Bad-Customer-Experience-Service-Engine-Light&p=150334#post150334

Correct nozzle placement (A):
Volt_Fuel_Neck.jpg

What kind of gasoline should I put in the Volt?
"Top Tier" detergent, 91 octane premium.

Owner's Manual:
Use of the recommended fuel is an important part of the proper maintenance of this vehicle. To help keep the engine clean and maintain optimum vehicle performance, we recommend the use of gasoline advertised as TOP TIER Detergent Gasoline.

Use premium unleaded gasoline with a posted octane rating of 91 or higher. If the octane is less than 91, you could damage the engine. If heavy knocking is heard when using gasoline rated at 91 octane or higher, the engine needs service.

To help keep fuel injectors and intake valves clean and avoid problems due to dirty injectors or valves, look for gasoline that is advertised as TOP TIER Detergent Gasoline. Look for the TOP TIER label on the fuel pump to ensure gasoline meets enhanced detergency standards developed by the auto companies.

What is Top Tier gasoline?
Top-tier is an industry program that defines a higher level of additives than required in "normal" fuel -- see www.toptiergas.com .


Why does GM recommend premium gasoline?
1. It's a five to ten percent fuel economy (MPG) improvement.
2. The help keep the engine fuel injectors and intake valves, etc. clean.
3. A longer shelf life.

The Volt engine operates over 2 very narrow RPM ranges and is optimized with Premium fuel for the most efficient operation. The Volt's timing and high compression ratio engine (10.5:1) run most efficiently using premium gasoline. Premium has a higher octane rating which is preferred for engines having higher compression ratios.

Higher octane gasoline resists self combustion longer, so it gives the piston a nice push during the power stroke, instead of an early bang. More compression = more heat. In a gas engine you want the spark to ignite the fuel mixture but if your compression ratio is too high you will generate too much heat and the fuel will self combust before the spark can ignite it (known as engine knock). The octane rating of fuel is just a measure of resistance to self combustion.
See http://gm-volt.com/forum/showthread.php?62561-Quick-Premium-Fuel-Question&p=813481#post813481

The self combustion resistance allows a higher compression ratio, all of which extracts more of the energy from the gasoline as kinetic energy, and less as waste heat. This apparently gives a smaller, more efficient Volt engine more torque, which is what a generator needs.

Also, higher octane fuels generally do not degrade to an unusable condition as rapidly as "regular" unleaded gas. If you start with 91 octane, it takes longer for that fuel to degrade to an unusable octane than it would for 87 octane. So premium will last longer while stored for long periods in the Volt's pressurized gas tank.

Still not convinced? According to Pam Fletcher the chief GM Powertrain Engineer for the Volt, they elected to use premium because it produced 10 to 15% improvement in range over regular.

Here's an old video where she discusses this issue (Powertrain Deep Dive Part 1). The premium fuel issue is discussed at about 4:27 into the video. If you haven't seen this series, it well worth seeing all three parts.


And Volt vehicle line director Tony Posawatz said, “The Volt is all about efficiency,” he said. “Premium fuel offers the opportunity to have a little bit more spark.”

“Ninety one octane fuel also offers the opportunity to be a little more efficient, he added. “So technically its a five to ten percent fuel economy improvement the few times that most people will run the range extender.”

Posawatz also claimed the increase in cost will be offset by the efficiency gains. “Based on our calculations the fuel economy and efficiency gains you get will effectively compensate for the extra cost of premium fuel,” he said.

Additionally, premium fuel is apparently slower to go stale. "If people are not using the extended range capability a lot, the premium fuel does last a little longer,” he said.
See http://gm-volt.com/2010/07/30/why-the-volt-requires-premium-gasoline/

Is octane the same as BTU (energy content)? Does higher octane mean more energy?

No. Octane is only a measure of how resistant a fuel is to pre ignition, not a measure of energy. It is a measurement of how sensitive the fuel is exploding (prior to the spark) due to high compression heat. Higher octane fuel may even have slightly less BTU (energy) content.

Premium does not have a higher BTU content, so why not use regular gasoline?

The higher BTU of regular is offset by the efficiency hit produced by the anti-knock controls.

There is not much of a BTU difference between Premium and Regular gas. If anything Premium might have slightly less BTU content than regular gas. Also, Premium fuel is naturally dirtier than Regular fuel so it requires additional detergents and additives (which does incidentally lead to a little better shelf life).

However changing the ignition timing has a very large influence on power and fuel economy.

Ideal ignition is not TDC (Top Dead Center), it is before TDC. The reason is the time required for the combustion pressure wave to reach the piston head. That is what you want to occur at or slightly ATDC.

As the RPMs increase the physical time decreases for the piston to reach TDC so the timing advances, because gasoline combusts at a constant rate, sometimes upwards of 60 degrees for 10+K RPM engines. At low RPM's with 10 degrees advance 87 octane is OK. At that speed, the heat/air compression rise is not sufficient to cause spontaneous combustion.

The important thing for an efficient power generation is flame travel. Otto cycle engines (such as the Volt's) are most efficient when the flame travels from the ignition source, the spark plug, towards the piston head.

As the compression heat rises faster from faster RPMs the lower octane (regular gasoline) is not able to resist spontaneous combustion in engines above about a 9.5/1 compression ratio. The problem is the flame travel is now from the source of the spontaneous combustion, not the intended point of ignition and at an uncontrolled point in the compression stroke. Worst case is spontaneous combustion near the piston head because the flame now is traveling towards the cylinder head when the spark initiated combustion occurs at the other end of the cylinder. But regardless of where is occurs when the two waves hit each other the pressure has to redirect itself and this is the source of the audible knock/ping. Timing is retarded to eliminate this to the point where the uncontrolled combustion is complete before the spark. Lousy for efficiency but less likely to cause damage.

Since the Volt was calibrated to run on premium fuel, this retarded timing to compensate for using regular fuel has a big effect on power and efficiency. If you live in area's that are normally cooler and/or higher altitudes with less air density you likely won't see too much of a difference between regular and premium fuels. But in warmer climates and/or with higher density air (closer to sea level) the difference will likely be much more noticeable.

Keep in mind the Volt's ICE is not direct injected. Direct injection might allow the engine to run on regular fuel without modified ignition timing. Hopefully Gen 2.0 will utilize this.

The Prius uses a sort of fake Atkinson cycle where it keeps the intake valve open for a portion of the beginning of the compression stroke effectively reducing the actual compression ratio while allowing for a longer power stroke. Even if the Volt were to do this in some scenarios, it is calibrated for premium fuel.
See http://gm-volt.com/forum/showthread.php?62561-Quick-Premium-Fuel-Question&p=813249#post813249

What if I accidentally filled up with regular?
Your mileage will suffer. You'll be OK, but you should not make a habit of it. The owner's manual recommends adding premium as soon as possible.

The Volt engine has an anti-knock system that allows the "occasional" use of regular in a pinch. It will modify the timing slightly to prevent premature detonation of the lower grade gasoline. However, with retarded timing comes more fuel consumption (lower MPG). A noticeable decrease in power and mileage after an accidental fill up with regular have been reported.
See http://gm-volt.com/forum/showthread.php?62993-Premium-Gas&p=819753#post819753,
also http://gm-volt.com/forum/showthread.php?11648-Premium-vs.-Regular-Gas&p=120301#post120301
and http://gm-volt.com/forum/showthread.php?19235-Fill-it-up-Super-please.&p=220622#post220622
and http://gm-volt.com/forum/showthread.php?19235-Fill-it-up-Super-please.&p=220631#post220631
and http://gm-volt.com/forum/showthread.php?45041-Gas-for-quot-High-Volume-quot-Users-Is-Premium-Top-Tier-Still-Required&p=588785#post588785
and http://gm-volt.com/forum/showthread.php?45041-Gas-for-quot-High-Volume-quot-Users-Is-Premium-Top-Tier-Still-Required&p=667257#post667257

Other's claim no effect.
See http://gm-volt.com/forum/showthread.php?62561-Quick-Premium-Fuel-Question&p=814025#post814025
and http://gm-volt.com/forum/showthread.php?55225-Who-uses-regular-gas&p=722361#post722361
and http://gm-volt.com/forum/showthread.php?45041-Gas-for-quot-High-Volume-quot-Users-Is-Premium-Top-Tier-Still-Required&p=588537#post588537
and http://gm-volt.com/forum/showthread.php?45041-Gas-for-quot-High-Volume-quot-Users-Is-Premium-Top-Tier-Still-Required&p=667569#post667569

You don't just lose efficiency when the timing is retarded, exhaust temperatures are elevated and your converter is stressed. In an EREV running CS mode the ICE is running at near maximum output (full-throttle) continuously to charge the battery. Unlike a conventional vehicle, the driver is not controlling and varying the engine throttle. In addition to the reduced efficiency, continuous knock control under this condition could have detrimental effects on other vehicle systems. For example – the rich fuel/air ratio could overheat and damage the catalytic converter.
See http://gm-volt.com/forum/showthread.php?6396-2-hopefully-quick-questions&p=55898#post55898

The other reason is GM wants the additives from premium fuel to reduce oxidation/moisture for fuel that may be there for months. GM took some heat for going with premium, it was not arbitrary. But if you want to volunteer your car to be a test case for whether regular harms the engine, well, it's your car.

Can the Volt use E85 flex-fuel gasoline?
No.

The car is not E85 capable according to the manual, that states only to use Premium Unleaded Top Tier Gasoline, at least 91 octane. When asked if an ethanol option for the Volt is likely, Brita Gross, the director of electric vehicle infrastructure and commercialization at General Motors, responded, "Nasaman, not at this time. The limited network of E85 refueling stations for consumers didn't justify the additional cost associated with adding the technology."

Because it is highly corrosive, using E85 takes a lot of special precautions, and seal/rubber selections inside the drive train. Not to mention the ECU/timing changes, and of course halving your oil life expectancy. Also, E85 has less energy per gallon than gasoline. So, MPG would drop too. "At its current price per gallon, E85 doesn't save you money, and it might cost you more. As of December 2010, a gallon of E85 was approximately 13 percent less than the cost of a gallon of gasoline nationally, according to e85prices.com. However, E85 produces 27 percent less energy per gallon than gasoline, so on average it ends up costing more."
See http://www.cars.com/go/advice/Story.jsp?section=fuel&subject=fuelAlt&story=e85


The primary differences from non-flex fuel vehicles is the elimination of bare magnesium, aluminum, and rubber parts in the fuel system, the use of fuel pumps capable of operating with electrically conductive (ethanol) instead of non-conducting dielectric (gasoline) fuel, specially-coated wear-resistant engine parts, fuel injection control systems having a wider range of pulse widths (for injecting approximately 60% more fuel), the selection of stainless steel fuel lines (sometimes lined with plastic), the selection of stainless steel fuel tanks in place of terne fuel tanks, and, in some cases, the use of acid-neutralizing motor oil. For vehicles with fuel-tank mounted fuel pumps, additional differences to prevent arcing, as well as flame arrestors positioned in the tank's fill pipe, are also sometimes used.
See http://gm-volt.com/forum/showthread.php?8567-When-will-the-Volt-run-on-E85-gasoline&p=81042#post81042

Can the Volt's engine emulate the Atkinson cycle?
Maybe? The Volt's engine is an Otto cycle, not an Atkinson cycle but a GM rep hinted that in certain (not specifically described) portions of the power map the Volt uses cam timing to emulate an Atkinson cycle.
See http://gm-volt.com/forum/showthread.php?11648-Premium-vs.-Regular-Gas&p=120358#post120358
and http://gm-volt.com/forum/showthread.php?11648-Premium-vs.-Regular-Gas&p=120417#post120417
Also see http://gm-volt.com/2009/12/15/chevy-volt-generator-does-not-use-the-atkinson-cycle/


Will I save money using regular instead of premium?
Probably not, and long term you may risk causing some damage or added maintenance expense.

For a car that uses very little gas to begin with, saving $20-$25/year by NOT using the recommended grade is unwise. As many have pointed out, why all the concern about saving very little money for an engine that most people only use only 20 - 30% of the time on average? It's not worth saving a few dollars per tank to get a gummed up engine or worse down the road.

Does higher alcohol content affect mileage?
Yes. The more alcohol, the lower the MPG.
See http://gm-volt.com/forum/showthread.php?11648-Premium-vs.-Regular-Gas&p=120354#post120354

Should I add fuel stabilizers like Sta-bil or other additives?
No. GM specifically warns against this.

Fuel stabilizes are not needed because the Volt will require a fuel burn before the gasoline would "go bad". Also, the pressurized gas tank helps minimize moisture intrusion (a well-known cause of stale gas), as well as prevent volitiles from evaporating from the gasoline.

What if I rarely use gasoline, won't the fuel eventually go bad regardless?
No. Before that would happen, the Volt will run engine maintenance (every 6 weeks if you don't use the engine) and fuel maintenance modes (yearly if you don't burn enough gas) to keep your engine lubricated and to keep your gas from going stale. It will also run intermittently in the winter if the temperature drops to below 15°F or 25°F, depending on your model year.

I'm getting a message that my engine needs to run, what's Engine Maintenance Mode (EMM)?
If the engine doesn't run for 6 weeks, the car will call for Engine Maintenance Mode (EMM). It runs the engine for a couple minutes to get everything up to temperature, drive water out of the oil, and re-lubricate cylinder walls, pistons, etc. If you drive in extended range mode for more than a few miles, the clock for EMM resets. The engine may also run in the winter with very short ICE burns with the message Engine Running Due to Low Temperature (ERDTLT).

How does the gasoline tank pressurization work?
The tank has a bladder that it is pressurized on the outside to squeeze air away from the gasoline. That technique comes from racing. The tank is evacuated via a vacuum pump prior to opening the filler door.
See http://gm-volt.com/forum/showthread.php?18868-Can-you-drive-a-Volt-without-any-gas-in-the-tank&p=215984#post215984

Can I run the Volt with no gasoline in the tank?

In an emergency, yes. Note that the Volt will go into a reduced propulsion mode when the tank is empty (a much slower gas pedal and limits power output) .The car is still drivable, even at freeway speeds, but it is much slower - even slower than a Prius, haha. And it will bug you to death reminding you to put some gas in the tank.
See http://gm-volt.com/forum/showthread.php?66754-I-RAN-THE-ICE-TIL-IT-WAS-EMTY

The official recommendation of the owner's manual is: "If fuel is not regularly used, consider keeping the fuel tank only one‐third full." Having a full tank is also an insurance policy in case of a natural disaster that knocks out electric service for many days.

Though it's not a good idea to run it with an empty tank, according to the Volt service manual, "The engine control module (ECM) supplies voltage to the fuel pump control module when the ECM detects that the ignition is on. The voltage from the ECM to the fuel pump control module remains active for 2 seconds, unless the engine is in crank or run. While this voltage is being received, the fuel pump control module supplies a varying voltage to the fuel tank pump module in order to maintain the desired fuel pressure." It sounds like the fuel pump isn't commanded to run unless the ignition to the ICE is turned on.

For one member's experiment running the tank dry, see http://gm-volt.com/forum/showthread.php?18761-Gasoline-range-following-quot-Low-Fuel-quot-indicator-and-running-out-of-gas/

Can I siphon the gasoline from my Volt's tank?
No. See http://gm-volt.com/forum/showthread.php?15865-Cannot-siphon-gas-out-of-my-Volt/

When the dash switches to the gasoline icon, am I using gas?
No, but the Volt is now in a "use the ICE when needed" mode. Even if your blue fuel icon is displayed, it does not mean the engine is running. The blue fuel icon vs the green battery icon indicates the mode of operation for the system. The vehicle will use all of the energy you put into the battery during charging before running the ICE. Any additional charge created during this mode (i.e. regen brakes), is tracked as gas miles. Therefore, when going back to normal, the additional charge is used first and tracked as gas miles.


Why am I Using .5 Miles of Gas with a full battery?
It's complicated. This is a feature of the vehicle which protects the battery from overcharging. Under certain circumstances, the electric motors will resist one another to provide braking in addition to the friction brakes on the vehicle. In order to meet emission requirements, the Volt does not spin the engine, but uses clutch 2 in the drive unit to link both motors. When the vehicle is at low speeds, clutch 2 requires that the resultant planetary gear set speeds increase to compensate. You will hear the electric motors at higher speeds, which is certainly a change from their normally silent operation.

The Volt was validated using the steepest, longest descent in the nation, Pike's Peak. With a full battery, the volt can descend Pike's Peak without issue with a combination of friction brakes and the electric motors. This is part of the Voltec propulsion system.

Related Posts:
Premium vs. Regular: the never ending question
http://gm-volt.com/2010/07/30/why-the-volt-requires-premium-gasoline/
http://gm-volt.com/forum/showthread.php?11648-Premium-vs.-Regular-Gas/
http://gm-volt.com/forum/showthread.php?62561-Quick-Premium-Fuel-Question/
http://gm-volt.com/forum/showthread.php?62993-Premium-Gas/
http://gm-volt.com/forum/showthread.php?19235-Fill-it-up-Super-please./
http://gm-volt.com/forum/showthread.php?55225-Who-uses-regular-gas/
http://gm-volt.com/forum/showthread.php?45041-Gas-for-quot-High-Volume-quot-Users-Is-Premium-Top-Tier-Still-Required/
http://gm-volt.com/forum/showthread.php?12888-Electrical-Noise-and-Premium-Fuel/
http://gm-volt.com/forum/showthread.php?14127-Volt-Newbie-two-questions/
http://gm-volt.com/forum/showthread.php?6396-2-hopefully-quick-questions/
http://gm-volt.com/forum/showthread.php?18111-Premium-Gas-Or-Regular-Gas-On-Very-Long-Trip/
Atkinson
http://gm-volt.com/2009/12/15/chevy-volt-generator-does-not-use-the-atkinson-cycle/
E85
http://gm-volt.com/forum/showthread.php?9566-E85/
http://gm-volt.com/forum/showthread.php?8567-When-will-the-Volt-run-on-E85-gasoline/
Run the tank dry
http://gm-volt.com/forum/showthread.php?18868-Can-you-drive-a-Volt-without-any-gas-in-the-tank/
http://gm-volt.com/forum/showthread.php?18761-Gasoline-range-following-quot-Low-Fuel-quot-indicator-and-running-out-of-gas/
Over-pumping, forced pumping, topping off
http://gm-volt.com/forum/showthread.php?15169-Ongoing-fuel-system-problem-since-new...now-worse-since-we-left-on-trip...&p=167775#post167775
EMM and ERDTLT
http://gm-volt.com/forum/showthread.php?66658-ICE-starting-for-maintenance/
http://gm-volt.com/forum/showthread.php?19923-ERDTLT-empty-gas-tank&highlight=empty+gas+tank
Siphoning Gas
http://gm-volt.com/forum/showthread.php?15865-Cannot-siphon-gas-out-of-my-Volt/
Gas vs. Battery Mode, ICE Miles
http://gm-volt.com/forum/showthread.php?65482-Gas-mileage-increase-while-on-battery&p=892697#post892697
 

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So I guess when someone asks me "where is it written?" I can either refer them here, or to the Dead Sea Scrolls...

Thanks... but for the two people who might ask, "Where did Steverino find the written part for this?" I have no idea what to tell them except maybe seek guidance from Baabaa Streisand.
 

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Discussion Starter #4
Yes, sorry for the length. That's why I broke it into the "yes/no" executive summary (because we Volt owners are all executives who make $175k/yr or more, haha), and then the more detailed post for those who want to know where the answer came from, the ins and outs, references, etc.

The number of posts about whether to use premium or regular is incredible, given that the owners manual clearly says "premium".
 

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Here is the reply I got from Costco regarding their "Clean Power" fuel vs "Top Tier":

Thank you for your inquiry about Costco gasoline!

In order to qualify for Top Tier an additive must contain about three times the EPA detergent requirement, and Costco's Clean Power dosage is five times the requirement. However, the physical quantity of additive is only one measure. The quality of the detergent can affect the amount of additive needed to meet the government requirement. The EPA standard is performance based, i.e., they require only the amount needed to keep engines at a certain level of cleanliness. Costco has tested our Kirkland Signature Clean Power detergent so our "5x" claim is performance-based.

Another Top Tier requirement is that it be available in all a company's fuel nation-wide. Costco does not yet have Clean Power installed at all of our U.S. gas stations. We plan to do so as fast as we can, at which time we will investigate whether to seek the official "Top Tier" designation. The Top Tier program is administered by General Motors, and supported by several other automakers such as Toyota, Honda, BMW, VW, and Audi.

A list of Kirkland Signature Clean Power locations can be found at costco.com by searching 'Clean Power' or by following this link: http://www.costco.com/clean-power-locations.html. With just a few exceptions, all US gas stations outside of California are now selling Clean Power fuel. We hope to have California complete in early 2014, but the process has been far longer in California than anywhere else.
 

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The number of posts about whether to use premium or regular is incredible, given that the owners manual clearly says "premium".
What is incredible is that someone would try to save 5c and risk damaging their car. Same thing with the quality of engine oil.

I learned a long time ago to not use 20w50 or any additional additives if the engine is spec'd for something else. The engineers know more about their build than some guy at the auto parts store.
 

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Discussion Starter #7 (Edited)
What is incredible is that someone would try to save 5c and risk damaging their car. Same thing with the quality of engine oil.

I learned a long time ago to not use 20w50 or any additional additives if the engine is spec'd for something else. The engineers know more about their build than some guy at the auto parts store.
Agreed. I calculated that ignoring GM's engineers and using regular would "save" me about $25/year. Of course it may cost me more long term for earlier engine maintenace and repair at the dealer, and my dealer charges $135/hr. So any "savings" would quickly vanish into my dealer's pocket. Then there is the cost of lower MPG that results from using regular (some exceptions are noted, possibly due to higher elevations).
 

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What is incredible is that someone would try to save 5c and risk damaging their car. Same thing with the quality of engine oil.
...
Maybe where you live. In northern California it's $0.20-0.40/gallon difference between 87 and 91 octane. But I wouldn't use 87 anyway. Because you cannot directly notice the difference in a Volt you might not think there is one. But if you have ever owned a turbocharged or supercharged engine then you do understand the difference.
 

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What is incredible is that someone would try to save 5c and risk damaging their car. Same thing with the quality of engine oil.
It's actually closer to $2 per tank, so it is dependent on how much gasoline you use.

Also, GM engineers have stated that there is roughly a 10% increase in fuel economy by using premium; however, that has been completely unverified by real-world testing. I, personally, have run three or four tanks of 87 octane through my Volt, and the mileage numbers have been indistinguishable between 87 and 91 (and even 93 for that matter) octane. And my experiences have been mirrored by others who have also used 87 octane in their Volts. Now, I can't speak to the long-term effects of running 87 octane, but for the short period I ran it, the mileage was unchanged from 91 octane.
 

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Steverino,

I have a PhD in chemistry, and I managed the advanced fuels research program for a major petroleum company before retiring 5 years ago. Normally the things one reads on forums like this are full of inaccuracies and statements that are just wrong. Yours was a refreshing read. You got things right! Good job!
Fuelscience
 

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I wonder at some point if the check engine light will be activated if you continue to use 87 Octane gasoline and the
engine possibly, over time, switching to reduced propulsion mode in certain cases.
 

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Steverino,

I have a PhD in chemistry, and I managed the advanced fuels research program for a major petroleum company before retiring 5 years ago. Normally the things one reads on forums like this are full of inaccuracies and statements that are just wrong. Yours was a refreshing read. You got things right! Good job!
Fuelscience
Thanks for validating the info! However, the attaboys go to the members of GM-Volt who have fleshed out this topic over many posts and threads. I merely did the research, gathered it all in one place, compiled and edited it. In the process, I usually learn a thing or two that I did not know before.



I wonder at some point if the check engine light will be activated if you continue to use 87 Octane gasoline and the engine possibly, over time, switching to reduced propulsion mode in certain cases.
I suspect the more likely short term outcome is poorer mileage, and worst case longer range is earlier engine maintenance expenses or repair. As I mentioned, buying regular would save me $20-$25/year. Not worth a potential 5-10% reduction in mpg or earlier engine repair. My dealer charges 6 years worth of savings per hour for engine repair, plus parts. I'm sticking with premium.
 
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