Author Topic: True or False? The case for Premium gas  (Read 12540 times)

Sarita

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True or False? The case for Premium gas
« on: November 30, 2014, 04:57:22 PM »
My normally frugal boyfriend puts premium gas in his 2003 VW Jetta Wagon.  He says the manufacturer strongly recommends it and that it prolongs the life of the car.

I know nothing about cars, and no one else I know uses anything but the most basic gas.  When I fill up his car for him, it kills me to use Premium but I suck it up and do it as it's his preference and his car.

So... what's the deal?  Is this true or just marketing on behalf of the gas companies?

wwweb

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Re: True or False? The case for Premium gas
« Reply #1 on: November 30, 2014, 05:25:29 PM »
When recommended by the manufacturer, premium gasoline is needed to prevent engine knock (which is caused by premature combustion during fuel compression).  Knock can damage the engine or cause it to run less efficiently.  Here is a more detailed explanation:
http://oppositelock.jalopnik.com/the-truth-about-gas-does-premium-fuel-perform-better-1487358722

You should keep using premium in your boyfriend's car.

For cars that do not require premium gasoline, the engine is optimized for regular (87 octane) fuel and using premium fuel is a complete waste.

Sarita

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Re: True or False? The case for Premium gas
« Reply #2 on: November 30, 2014, 05:26:56 PM »
Thanks, wwweb, your explanation makes sense.  Thank you!

Primm

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Re: True or False? The case for Premium gas
« Reply #3 on: November 30, 2014, 05:50:50 PM »
FYI, this is what happens when you put non-premium fuel in your car (if the car requires premium).

A preventable cracked engine block is particularly un-Mustachian, I would suggest. :)

netskyblue

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Re: True or False? The case for Premium gas
« Reply #4 on: November 30, 2014, 06:36:51 PM »
I've heard that gas mileage is better with the non-ethanol gas (which is the cheapest here in IA, it's subsidized).  I've also been advised to avoid it in the winter, not sure why.

chucklesmcgee

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Re: True or False? The case for Premium gas
« Reply #5 on: November 30, 2014, 07:56:36 PM »
using premium fuel is a complete waste.

Not only does it provide no benefits for a car that doesn't require it, higher octane fuel actually has less energy per gallon than regular, so you'll be paying more money to get a slightly lower mileage out of it!

Primm

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Re: True or False? The case for Premium gas
« Reply #6 on: November 30, 2014, 08:34:30 PM »
using premium fuel is a complete waste.

Not only does it provide no benefits for a car that doesn't require it, higher octane fuel actually has less energy per gallon than regular, so you'll be paying more money to get a slightly lower mileage out of it!

That's the point though, some cars are designed to use premium and will sustain engine damage if you don't use it.

I have a car that doesn't care, as long as I use a lead substitute additive. I did comprehensive MPG calculations over a period of 2 years, and my individual car gets better mileage from premium. The cutoff for me is about 7% dearer (yes, I did drill down that far - stats geek!), after which point regular unleaded is more cost-effective.

It depends on the individual car. The OP's partner's car requires premium ULP, so they'd be risking potentially expensive damage to save a few cents per litre.

m8547

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Re: True or False? The case for Premium gas
« Reply #7 on: November 30, 2014, 09:19:11 PM »
I've heard that gas mileage is better with the non-ethanol gas (which is the cheapest here in IA, it's subsidized).  I've also been advised to avoid it in the winter, not sure why.

I tested this for one tank. There was no measurable difference, and if anything the mileage was slightly worse than expected. In theory 100% gas should give you about 3.5% more mileage than 10% ethanol/90% gas, if I did the math right. That's within the noise for my fuel economy measurements.

deborah

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Re: True or False? The case for Premium gas
« Reply #8 on: November 30, 2014, 09:25:22 PM »
I've heard that gas mileage is better with the non-ethanol gas (which is the cheapest here in IA, it's subsidized).  I've also been advised to avoid it in the winter, not sure why.

I tested this for one tank. There was no measurable difference, and if anything the mileage was slightly worse than expected. In theory 100% gas should give you about 3.5% more mileage than 10% ethanol/90% gas, if I did the math right. That's within the noise for my fuel economy measurements.
Depends on your car - the one I have just replaced was very very unhappy whenever it had the slightest whiff of ethanol

Primm

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Re: True or False? The case for Premium gas
« Reply #9 on: November 30, 2014, 09:36:46 PM »
I've heard that gas mileage is better with the non-ethanol gas (which is the cheapest here in IA, it's subsidized).  I've also been advised to avoid it in the winter, not sure why.

I tested this for one tank. There was no measurable difference, and if anything the mileage was slightly worse than expected. In theory 100% gas should give you about 3.5% more mileage than 10% ethanol/90% gas, if I did the math right. That's within the noise for my fuel economy measurements.
Depends on your car - the one I have just replaced was very very unhappy whenever it had the slightest whiff of ethanol

The age matters too. Anything with carburettors or any older components that contain brass will be destroyed by ethanol. It's highly hydrophilic, so it will rust away the internals of your fuel system.

That's a big problem for mustachian types who don't drive much too. Ethanol based fuel sitting in your tank will attract water from the air and can cause big problems if your car sits for periods of time without being used and without flushing fuel through the system by driving it frequently.

BlueMR2

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Re: True or False? The case for Premium gas
« Reply #10 on: December 01, 2014, 10:53:04 AM »
I've heard that gas mileage is better with the non-ethanol gas (which is the cheapest here in IA, it's subsidized).  I've also been advised to avoid it in the winter, not sure why.

I tested this for one tank. There was no measurable difference, and if anything the mileage was slightly worse than expected. In theory 100% gas should give you about 3.5% more mileage than 10% ethanol/90% gas, if I did the math right. That's within the noise for my fuel economy measurements.

The lower energy density of Ethanol not only reduces MPG slightly, but can confuse older cars.  During the transition period where I could get real gas at some places and E10 at others I was able to do a lot of experimentation.  34MPG on real gas, 32MPG on E10 for the daily commute.  The worst part though is that my car was designed for 87 octane, but on E10 I have to run 93 octane to avoid knock.  Real gas 87 was fine, but with ethanol the computer doesn't compensate and it knocks pretty bad (It's a 1991, so no knock sensor).

pzxc

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Re: True or False? The case for Premium gas
« Reply #11 on: December 01, 2014, 11:32:27 AM »
It's super annoying that in a lot of states you cannot buy gasoline without ethanol.  For example, in Florida and California, state law requires 10% ethanol in all consumer gasoline.

The only exception I know if is gasoline sold at marinas -- ethanol will dissolve through the (fiberglass) gas tanks of aquatic vehicles, so they are still allowed to sell "pure" gasoline there.

Gone Fishing

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Re: True or False? The case for Premium gas
« Reply #12 on: December 01, 2014, 11:39:38 AM »
Yet another reason not to buy a "high performance" vehicle.

Will

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Re: True or False? The case for Premium gas
« Reply #13 on: December 01, 2014, 12:04:02 PM »
For as long as I can remember, for some reason, premium gas has always been 20 cents higher per gallon than regular.  Back when regular was $1/gal, premium was $1.20.  Then it was $2 and $2.20, $3 and $3.20, and so on.  With the amount of driving I do, I average buying maybe 5 gallons of gas a week.  Buying premium (which my car requires) therefore costs about an extra dollar.  It most certainly is NOT worth risking major damage to my car's engine for one dollar.

Holyoak

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Re: True or False? The case for Premium gas
« Reply #14 on: December 01, 2014, 12:18:48 PM »
Lists stations that have pure, ethanol free gas:

http://pure-gas.org/

I used the site, found a station, but cost is WAY higher over their normal pump gas when you get there.  Interesting to note the site says ALL gasoline sold in AK is ethanol free.  As an aside, Aviation Gasoline "Avgas" is typically 100 octane low lead without any ethanol.  When I refueled aircraft for a living, we would allow folks who had a valid aircraft tail number, fill 5 gal jugs with 100LL...  Where it exactly went, I can't say... *COUGH* old muscle car, *COUGH*...

ketchup

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Re: True or False? The case for Premium gas
« Reply #15 on: December 01, 2014, 12:52:16 PM »
I've heard that gas mileage is better with the non-ethanol gas (which is the cheapest here in IA, it's subsidized).  I've also been advised to avoid it in the winter, not sure why.

I tested this for one tank. There was no measurable difference, and if anything the mileage was slightly worse than expected. In theory 100% gas should give you about 3.5% more mileage than 10% ethanol/90% gas, if I did the math right. That's within the noise for my fuel economy measurements.
Depends on your car - the one I have just replaced was very very unhappy whenever it had the slightest whiff of ethanol
Older cars care the most.  My old carbureted '88 I had until last year got almost exactly 10% better mileage with no-ethanol gas compared to 10% ethanol gas.  The engine seemed to enjoy life better too on the good stuff.

I still haven't had a chance to use verified no-ethanol gas with our current cars ('92 and '99).

Sid Hoffman

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Re: True or False? The case for Premium gas
« Reply #16 on: December 01, 2014, 01:27:47 PM »
My normally frugal boyfriend puts premium gas in his 2003 VW Jetta Wagon.

While you didn't say it, I am betting he's got one with the 1.8T engine, a relatively high compression (for its time) turbocharged engine.  Confirmed: the recommended minimum octane is 91 for that motor.  You can get away with running 89 in a pinch and technically it can (usually) run OK on 87 but it's just not a good practice to run older turbocharged engines on such low octane fuel.  89 would be the minimum I would be comfortable with and yeah, it really will run best on 91.

GetItRight

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Re: True or False? The case for Premium gas
« Reply #17 on: December 01, 2014, 01:40:09 PM »
Octane is essentially a measurement of resistance to ignition, such as from heat. High compression and more advanced ignition timing require a fuel more resistant to spontaneous ignition and with a slower more consistent burn rate. Without this there is preignition or detonation which will cause severe engine damage such as broken rings, rapid main and rod bearing wear, head gasket failure, etc...

Run the minimum octane recommended by the engine manufacturer. More octane won't hurt but offers no benefit, insufficient octane will get expensive pretty quick. For what it's worth, engines with greater compression but requiring premium fuel are generally a lot more efficient (more power and more MPG) than a lower compression engines that run on anything.

Holyoak

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Re: True or False? The case for Premium gas
« Reply #18 on: December 01, 2014, 02:11:04 PM »
Direct injection, and incredibly accurate/precise timing is really changing the game...  Stock 13:1 compression ratio NA, using 87 octane in a 2.5L Mazda "Skyactive" engine...  This is simply amazing, and inconceivable not so many years ago.  Many cars will use a knock sensor, and alter timing to suit to avoid damage, but performance really takes a hit.  Their new Diesel engine that is not here yet, is just as amazing for its low CR...  Neat stuff.

Sid Hoffman

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Re: True or False? The case for Premium gas
« Reply #19 on: December 01, 2014, 03:14:57 PM »
Direct injection, and incredibly accurate/precise timing is really changing the game...

Indeed, hence why I pointed out the 2003 Jetta used the 1.8T which while advanced for its time, it's actually an engine that actually dates back to 1999.  It's a port fuel injected turbo engine with 9.5:1 compression at a time when a lot of turbo engines had CRs in the 8's!  Go back to old turbo cars like the Porsche 930 and you'll see references to a 6.5:1 compression ratio for the 1975-76 model.  Technology has come a long way but the general rule of using the fuel recommended by the manufacturer still applies.

Eric

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Re: True or False? The case for Premium gas
« Reply #20 on: December 18, 2014, 09:59:17 PM »
After reading this thread, doing some outside reading, and with the recent super cheap gas, I finally took the plunge and bought a tank of premium.  I'm in a 2004 VW Passat with the 1.8L engine, recommended 91 octane I believe.  Well, I'm a half a tank in and my check engine light is on.  Coincidence?  Or a result of the engine having 135K miles of regular and now not knowing what to do with the good stuff?

Greg

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Re: True or False? The case for Premium gas
« Reply #21 on: December 18, 2014, 10:04:50 PM »
After reading this thread, doing some outside reading, and with the recent super cheap gas, I finally took the plunge and bought a tank of premium.  I'm in a 2004 VW Passat with the 1.8L engine, recommended 91 octane I believe.  Well, I'm a half a tank in and my check engine light is on.  Coincidence?  Or a result of the engine having 135K miles of regular and now not knowing what to do with the good stuff?

Unlikely, it could be anything.

DarinC

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Re: True or False? The case for Premium gas
« Reply #22 on: December 18, 2014, 11:36:47 PM »
Yeah, a CEL can be a bunch of things, pull the code and find out what it is.

Sid Hoffman

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Re: True or False? The case for Premium gas
« Reply #23 on: December 19, 2014, 12:21:09 AM »
Having a MIL (malfunction indicator lamp) on is just a way of reminding you that you have a Volkswagen.  Some VW owners have gone so far as to get the MIL as a tatoo.  It's also available as a T-shirt.

cartechguy

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Re: True or False? The case for Premium gas
« Reply #24 on: December 19, 2014, 06:14:54 AM »
Yes, yes, yes ONLY put what is recommended by what your owner manuals tells you.  It can get very technical for me to go into detail but, trust me and my 20+ years in the auto repair industry!!

If your car only tells you to put in regular gas ONLY do that or your wasting your money!

Many people don't think about what type of gas there car needs when buying a car!! Premium can drain you!!

Greg

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Re: True or False? The case for Premium gas
« Reply #25 on: December 19, 2014, 09:42:09 AM »
Another thing to look at is not just the number, but what measurement the number represents.  For instance, my VW Vanagon requires 91 RON (research octane number) which is equivalent to 87 (R+M)/2) as posted on pumps in the USA.  So, my engine only requires low octane fuel.

http://en.wikipedia.org/wiki/Octane_rating

Modifications like higher compression, different timing etc. usually require higher octane fuel.

US gas stations usually have 2 underground tanks, one of high octane and one of low octane, and they are mixed to supply the mid-grade octane.  Some engines have variable timing or knock-sense ignitions that will compensate for different octane fuels.  With these engines, if you buy higher octane fuel, you'll get better performance, but can run lower octane fuel if you want to.

eil

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Re: True or False? The case for Premium gas
« Reply #26 on: December 19, 2014, 11:29:01 AM »
The age matters too. Anything with carburettors or any older components that contain brass will be destroyed by ethanol. It's highly hydrophilic, so it will rust away the internals of your fuel system.

What? This simply isn't true. There are scads of vintage motorcycles (with brass jets in their carburetors) that have run 87 octane E10 since it's been available at the pumps with no issues whatsoever.

Ethanol does not corrode brass, neither does water. Water can corrode steel, but steel bits are few and far between in most fuel systems for this reason. In any event, the fuel would have to sit for a fairly long time in order for the ethanol to absorb enough water to matter and gas tends to evaporate much quicker than that.

Eric

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Re: True or False? The case for Premium gas
« Reply #27 on: December 19, 2014, 12:27:50 PM »
Thanks for the feedback Greg and Darin.  Yeah, I figured it was a coincidence too, but jeez, talk about bad timing.  I'm getting the oil changed on Tuesday, so I'll find out then. 

And thanks Sid, that's funny enough to make me cry.  ;)

BlueMR2

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Re: True or False? The case for Premium gas
« Reply #28 on: December 19, 2014, 01:48:06 PM »
The only exception I know if is gasoline sold at marinas -- ethanol will dissolve through the (fiberglass) gas tanks of aquatic vehicles, so they are still allowed to sell "pure" gasoline there.

Airports offering "mogas" are normally without ethanol as well, since *most* aircraft with STCs (FAA approved modifications) for use of gas other than the normal "avgas" are still not allowed any ethanol.  Exceptions off the top of my head are some experimentals with rotax engines.  So, you *may* find ethanol gas at an airport, but typically you wouldn't and either way it will be VERY clearly marked due to federal requirements.

APowers

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Re: True or False? The case for Premium gas
« Reply #29 on: December 19, 2014, 01:59:28 PM »
The age matters too. Anything with carburettors or any older components that contain brass will be destroyed by ethanol. It's highly hydrophilic, so it will rust away the internals of your fuel system.

What? This simply isn't true. There are scads of vintage motorcycles (with brass jets in their carburetors) that have run 87 octane E10 since it's been available at the pumps with no issues whatsoever.

Ethanol does not corrode brass, neither does water. Water can corrode steel, but steel bits are few and far between in most fuel systems for this reason. In any event, the fuel would have to sit for a fairly long time in order for the ethanol to absorb enough water to matter and gas tends to evaporate much quicker than that.

If I understand correctly, it's not a "ethanol facilitates rust", as much as "ethanol degrades rubber/gaskets/etc.". If what I was told a long time ago is true, newer cars/engines are designed to use alcohol-resistant gaskets/etc., while older vehicles weren't. Anecdotally, I've never noticed a problem with either my '71 VW Super Beetle or my '67 VW Type III.

Re OP-- I used to always run regular in my '71 VW, and then one day noticed that the fuel filler door called for 91. I already kept fairly religious track of mileage/fuel, so I switched to premium and continued tracking. Turned out that premium boosted the fuel economy just enough to cover the increased cost. Also, it ran better. So I used premium. Eventually spun out on black ice and ended up selling it, but that's another story.


alsoknownasDean

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Re: True or False? The case for Premium gas
« Reply #30 on: December 19, 2014, 03:14:51 PM »
The age matters too. Anything with carburettors or any older components that contain brass will be destroyed by ethanol. It's highly hydrophilic, so it will rust away the internals of your fuel system.

What? This simply isn't true. There are scads of vintage motorcycles (with brass jets in their carburetors) that have run 87 octane E10 since it's been available at the pumps with no issues whatsoever.

Ethanol does not corrode brass, neither does water. Water can corrode steel, but steel bits are few and far between in most fuel systems for this reason. In any event, the fuel would have to sit for a fairly long time in order for the ethanol to absorb enough water to matter and gas tends to evaporate much quicker than that.

Doesn't ethanol destroy any rubber components in the fuel system?

I have to admit I've been using premium gas in my previous cars (even 98RON in my previous car, but it required 95RON anyway and 98 was a few cents more, plus I liked getting extra range per tank.

With the new car, I've got a tank of regular 91RON unleaded in it. I've been kinda considering putting 95RON in it (because it was built in Europe and that's the standard fuel there, not sure if it was detuned to run on Aussie 91 octane fuel), but it runs fine with 91.

Not sure with E10. The car apparently supports it, so maybe it's worth a try later down the track. It's only a few cents cheaper than regular unleaded though.

using premium fuel is a complete waste.

Not only does it provide no benefits for a car that doesn't require it, higher octane fuel actually has less energy per gallon than regular, so you'll be paying more money to get a slightly lower mileage out of it!

That's the point though, some cars are designed to use premium and will sustain engine damage if you don't use it.

I have a car that doesn't care, as long as I use a lead substitute additive. I did comprehensive MPG calculations over a period of 2 years, and my individual car gets better mileage from premium. The cutoff for me is about 7% dearer (yes, I did drill down that far - stats geek!), after which point regular unleaded is more cost-effective.

It depends on the individual car. The OP's partner's car requires premium ULP, so they'd be risking potentially expensive damage to save a few cents per litre.

Interesting. I thought that the old leaded fuel was roughly equivalent in octane to premium anyway (I believe Super was 96RON), so I assumed that anything pre-1986 would require premium with the additive.
« Last Edit: December 19, 2014, 03:17:46 PM by alsoknownasDean »

Primm

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Re: True or False? The case for Premium gas
« Reply #31 on: December 19, 2014, 04:30:25 PM »
The age matters too. Anything with carburettors or any older components that contain brass will be destroyed by ethanol. It's highly hydrophilic, so it will rust away the internals of your fuel system.

What? This simply isn't true. There are scads of vintage motorcycles (with brass jets in their carburetors) that have run 87 octane E10 since it's been available at the pumps with no issues whatsoever.

Ethanol does not corrode brass, neither does water. Water can corrode steel, but steel bits are few and far between in most fuel systems for this reason. In any event, the fuel would have to sit for a fairly long time in order for the ethanol to absorb enough water to matter and gas tends to evaporate much quicker than that.

Whoops, sorry. Ethanol doesn't corrode brass, it corrodes the bits that connect to brass, and the newer components like plastic carb needles that replace the old brass ones.

http://www.mossmotors.com/SiteGraphics/Pages/ethanol.html

http://blog.hemmings.com/index.php/2012/11/14/tech-101-ethanol-in-gasoline-and-its-effects-on-collector-cars/

Wait, unless you believe the Indiana state government

Quote
Ethanol can accelerate corrosion in steel UST systems by scouring or loosening deposits on the internal surfaces of tanks and piping. If a corrosion cell exists, the ethanol can accelerate (scour) the corrosion cell and cause a perforation. As mentioned above, ethanol is not compatible with soft metals such as zinc, brass, copper, lead, and aluminum. These metals will degrade or corrode in contact with ethanol and possibly contaminate a vehicle’s fuel system.

http://www.in.gov/idem/files/la-072-gg.pdf

But nobody believes the government, right?

N=1 story - my stepson bought a 1990 Nissan Pintara that he had sitting for a while at our place while he was overseas. When he went to try it 6 months later the fuel system had devolved into a sludgy mess, and he had to wreck the car. Uneconomical to repair. We've restored dozens of old cars that have sat for ages with non-Ethanol based fuel in them, and up to 10 years later they've started. Not easily and not well, but it hasn't degraded the fuel system.

gimp

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Re: True or False? The case for Premium gas
« Reply #32 on: December 19, 2014, 05:19:30 PM »
I'm in the same boat - supercharged engine wants 91+. Thankfully the car is a new enough model that it compensates for low-octane fuel; sometimes in various parts of the country you can only get as high as 89... or 87... or 85... or 83... I tend to take eight-ten gallons of extra when driving there, but sometimes it's gotta be done. Basically the car upon detecting low octane fuel just doesn't turn the supercharger on. Done once in a while it's okay, often it'll be more of an impact.

Many compressors - superchargers, turbochargers, even engines that get the compression effect from a hood - want premium fuel.

Anything else and it's a waste of money unless you're specifically buying non-ethanol for a good reason. New cars don't mind ethanol. Old ones sure do.

Sid Hoffman

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Re: True or False? The case for Premium gas
« Reply #33 on: December 22, 2014, 09:09:21 AM »
New cars don't mind ethanol. Old ones sure do.

For 15 years or so California has been mixing Ethanol into seasonal fuel and for the last 8 or so since MTBE was banned ethanol has been in the year-round blend.  There are probably more regularly driven classic cars in California than anywhere in the world.  Ethanol is bad for some gaskets and hoses, but those are a wear item you have to replace ever so often on any car.  If ethanol simply destroyed older cars outright, or was an impossible maintenance headache to deal with then you'd have no more classic cars in California anymore.  Instead people just buy new fuel lines and gaskets whenever needed and go on with life.

For things like boats and aircraft where they used materials in the fuel tanks themselves which could degrade (boats especially, as they used to be commonly built with with unlined fiberglass fuel tanks) the issues are a little more complex.  Removing the tank on a boat or replacing "wet wings" on an aircraft can turn out to be impossible or at least impractical.  We're talking about cars here in this thread though.  Ethanol, because it's a great solvent, is actually a pretty good additive to gasoline because of the fact it eats away at a lot of things that can otherwise gunk up the fuel system.  I just wish it was used in a lower concentration, like 3-5%.  Our current government requirements have had ethanol in direct competition with food production for several years now with no meaningful clean air benefit in this age of emissions already being so clean to begin with thanks to ever-tightening EPA laws.

ksoto

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Re: True or False? The case for Premium gas
« Reply #34 on: December 25, 2014, 05:21:56 AM »


 For things like boats and aircraft where they used materials in the fuel tanks themselves which could degrade (boats especially, as they used to be commonly built with with unlined fiberglass fuel tanks) the issues are a little more complex.  Removing the tank on a boat or replacing "wet wings" on an aircraft can turn out to be impossible or at least impractical.   

I can back Sid up on the incompatibility of fuel tanks. I spent 15 years building an airplane in my garage. There was no ethanol in auto gas when I started building and the resins used in the fiberglass tanks can't handle it. They are buried in the wings and can't be replaced easily. So even though I have an aircraft engine that can burn premium auto gas, I can't use it. Stuck using aviation fuel which is VERY expensive. But I use it mostly to travel and most airports don't have auto gas anyway and I would be forced to buy avgas regardless.