What octane gas do you use to fill your car?

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What octane gas do you use to fill your car?

87
141
75%
89
9
5%
91
13
7%
93
25
13%
 
Total votes: 188

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xzhou
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What octane gas do you use to fill your car?

Post by xzhou »

I drive a Lexus ES 330 as a commute car everyday, and usually fill it with 87 gas, which gives me close to 24 mpg. Last time when I filled it, I accidentally picked up a 91 pump. I am now pleasantly surprised by a 28 mpg reading. The price difference is 10%, but the mpg improvement is better than 15%. Is this related to warmer weather? Should I switch to 91 forever?
[EDIT] :oops: I was reading MPH, not MPG. There is no difference between 87 and 91 in gas mileage.
Last edited by xzhou on Mon Jun 16, 2014 12:05 pm, edited 1 time in total.
Angelus359
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Re: What octane gas do you use to fill your car?

Post by Angelus359 »

That's a fluke.

Higher octane, in a car designed for 87, actually will give you worse fuel efficiency, with no additional power. Octane rating is just resistant to pre-mature detonation. Higher octane fuels allow for higher compression ratios. If your car doesn't have that higher compression ratio, it does nothing but slow down the burn speed, which reduces power output and fuel efficiency.

It's probably the warmer weather.
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tim1999
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Re: What octane gas do you use to fill your car?

Post by tim1999 »

My cars all require 91 octane minimum. They don't sell 91 in my area, only 92 or 93, so I go with those.

I used to have a few cars where 91 minimum was recommended but not required. Those cars got about 2mpg worse on 87 for similar driving, and I only used the 87 if premium was sold out or whatever. If I floored the pedal from a stop with the 87, it just felt slightly less powerful - car was a turbo and it felt like it bogged down a bit before the turbo would spool up.

I've also noticed that if I can find ethanol-free gas (very rare in PA these days) I get a couple MPG higher, though once again, the fuel is more expensive, so it's probably a wash.
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HardKnocker
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Re: What octane gas do you use to fill your car?

Post by HardKnocker »

Manufacturers tell you what octane to use in your car. It's in the manual.

Some cars prefer regular.
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investingdad
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Re: What octane gas do you use to fill your car?

Post by investingdad »

Both my cars require Premium, one is a V6 and the other is turbo-charged.

My wife's car is a 4 cylinder and gets regular.
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bottlecap
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Re: What octane gas do you use to fill your car?

Post by bottlecap »

xzhou wrote:I drive a Lexus ES 330 as a commute car everyday, and usually fill it with 87 gas, which gives me close to 24 mpg. Last time when I filled it, I accidentally picked up a 91 pump. I am now pleasantly surprised by a 28 mpg reading. The price difference is 10%, but the mpg improvement is better than 15%. Is this related to warmer weather? Should I switch to 91 forever?
Gosh, your mileage will very every tank, depending on how you drive and the routes you take. I don't think a higher octane gives any better gas mileage, but even if it does, it wouldn't give you that much better and, in any event, you shouldn't exceed what your car's manual says to use. It will cause more problems than that outweigh any benefits, real or imagined.

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Re: What octane gas do you use to fill your car?

Post by MrBachelor »

The required fuel for my car is 91 and I never use anything less. I drive a 2006 Lincoln LS. I would love to save a few bucks at each fill but am not willing to risk damage to the car or reduced power/performance of the engine.
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Re: What octane gas do you use to fill your car?

Post by tomd37 »

In my cars I use whatever octane is called for in the owner's manual. In the case of my 2001 Lexus ES300 it is 87 octane. I believe Lexus calls for 87 in all ES model years since that time. Every article I have ever read says using a higher octane does not bring any overall gain considering performance and price as today's engines automatically adjust to the requirements at the moment.

I have kept an auto mileage record book on every vehicle we have owned since 1975 and record the miles driven and gasoline consumed at each filling. I do not depend on any instruments provided in the car as they are never correct when it comes to miles per gallon.

Some cars such as my 2010 Volkswagen Passat 2.0T station wagon did require the higher octane because of its particular engine and that is what I used when I owned it.
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Re: What octane gas do you use to fill your car?

Post by izreel »

I go with what my can requires. 91.
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FrugalInvestor
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Re: What octane gas do you use to fill your car?

Post by FrugalInvestor »

It's all very complicated with today's engineering and there is not one simple answer. This article gets into some of the details if you're interested....

http://www.roadandtrack.com/go/news/new ... el-futures

Personally I've done done fine with regular even in vehicles where premium is recommended. I put 140,000 miles on a Lexus RX330 we once owned using regular when premium was recommended with absolutely no ill effects - it was the most reliable vehicle I've ever owned never needing anything but routine maintenance. My mileage was above the vehicle's rating - although YMMV (pun intended). I tried a couple of tanks of premium early on and noticed no improvement. I also use regular in our current Acura vehicle for which premium is recommended and my highway mileage (which I track most closely) is above the manufacturer's rating. In my past and present high performance sports cars however, I use premium as recommended figuring that the engines are more finely tuned.
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Re: What octane gas do you use to fill your car?

Post by Grt2bOutdoors »

What the manual says, to put in a more expensive grade is just throwing money out the window. The difference between 87 and 91 or 93 can be fifty (50) cents or more per gallon. For that extra $10, I can pick up an extra .22 or .30 shares of Total Stock Market or Total International (you read it right, I said "point"), over time that can be a significant amount of :moneybag.
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Re: What octane gas do you use to fill your car?

Post by midareff »

izreel wrote:I go with what my can requires. 91.

+1 ... dealer says you can get by with one in four being midgrade but I stay with premium.
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Re: What octane gas do you use to fill your car?

Post by jasc15 »

I just bought a used Volvo V50. I read a lot about how it requires premium gas, but the manual "recommends" 91 octane, and can use 87 with no problem. I've been using 87 since we got it. To the Lexus owner who used 91 instead of the 87, I would attribute the increased gas mileage to the warmer weather, since I have a noticeable increase in fuel economy the last few tanks without changing the octane. After a year of using 87, i will switch to 91 to see if there is a noticeable increase in fuel economy. I figure waiting a year will control for seasonal variations in fuel consumption.

Also, octane rating is measured differently in different countries. This is probably not relevant to most folks on this forum, but I learned about it when I downloaded an owner's manual for my car which showed the octane ratings using the Research Octane Number (RON) rather than the Anti Knock Index (AKI) used in the US. An AKI of 87 is the same as a RON of 92. So when the downloaded manual recommended a minimum of 92 octane, it was written for the european market. The one in the car was written for the US and the minimum was 87.
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Re: What octane gas do you use to fill your car?

Post by Random Poster »

You can buy (and, depending on the car, safely use) 85.5 octane fuel in Montana, Idaho, Wyoming, and other various mountainous locales.
Khanmots
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Re: What octane gas do you use to fill your car?

Post by Khanmots »

Angelus359 wrote:That's a fluke.

Higher octane, in a car designed for 87, actually will give you worse fuel efficiency, with no additional power. Octane rating is just resistant to pre-mature detonation. Higher octane fuels allow for higher compression ratios. If your car doesn't have that higher compression ratio, it does nothing but slow down the burn speed, which reduces power output and fuel efficiency.

It's probably the warmer weather.
This.

My car has a 11:1 compression ratio on a NA (naturally aspirated) engine. I don't put anything lower than 91 in it... (what the manual calls out) and since my local choices are 87, 89, or 93... 93 it is.

When I drive my parents 4-cyl accord it's 87 only, there's no purpose to higher other than potentially causing the engine to run sub-optimal (it's tuned for 87)
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Re: What octane gas do you use to fill your car?

Post by Woodshop2300 »

94-96, otherwise knows as E85.
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Re: What octane gas do you use to fill your car?

Post by pennstater2005 »

HardKnocker wrote:Manufacturers tell you what octane to use in your car. It's in the manual.

Some cars prefer regular.
Exactly. Same goes for all my other gas powered equipment.
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Re: What octane gas do you use to fill your car?

Post by Polymorphic »

My car runs fine on regular, though Honda has acknowledged that their V6 will produce a bit more horsepower using premium. I personally run 93 octane because at the nearby fuel station, it is ethanol-free, while the 87 and 89 octanes are not.
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Re: What octane gas do you use to fill your car?

Post by Epsilon Delta »

Jon wrote:My car runs fine on regular, though Honda has acknowledged that their V6 will produce a bit more horsepower using premium. I personally run 93 octane because at the nearby fuel station, it is ethanol-free, while the 87 and 89 octanes are not.
The OP might want to check on the ethanol content of his fuel. E0 has more energy per gallon than E90 or E85 so if the premium gas is ethanol free you would expect higher mpg.
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munemaker
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Re: What octane gas do you use to fill your car?

Post by munemaker »

xzhou wrote:I drive a Lexus ES 330 as a commute car everyday, and usually fill it with 87 gas, which gives me close to 24 mpg. Last time when I filled it, I accidentally picked up a 91 pump. I am now pleasantly surprised by a 28 mpg reading. The price difference is 10%, but the mpg improvement is better than 15%. Is this related to warmer weather? Should I switch to 91 forever?
You should use the octane specified in the owner's manual. Sometimes it is on the inside of the gas cap door.

If you achieved more mpg using 91 octane when the car calls for 87, then it is just a coincidence.

I used to own a 2000 Honda Civic Si. The Si has a 1600 cc engine that produces 160 hp and 8,000 rpm redline (5 speed trans). Manual calls for 91 octane. The manual said in a pinch, you could use 87. During one of the gasoline price run-ups, I experimented with that. Comparing carefully measured averages of several tanks, I found that mileage did not vary using the lower grade. What did vary was performance. The engine started and ran smoothly, but had absolutely no power. When I switched back to higher octane, the performance returned.

A word about ethanol. I asked a station operator about that one time, and he says the ethanol content can be up to 10% but varies by tanker load. He showed me that manifest and the ethanol content was specified on it. I don't know if all companies do that or not. So...you may think the gas you are buying has 10% ethanol, but it may have any amount between 0 and 10%. Yes, gas with ethanol gives fewer mpg...but it is not that significant up to 10%.
jasc15
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Re: What octane gas do you use to fill your car?

Post by jasc15 »

Why the aversion to ethanol?
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Re: What octane gas do you use to fill your car?

Post by fareastwarriors »

I think I have to use 91 for my Mini Cooper.
Don't see 93 around the stations where I go.
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Re: What octane gas do you use to fill your car?

Post by Spirit Rider »

jasc15 wrote:Why the aversion to ethanol?
Ethanol is used in gasoline as an oxygenate; provides oxygen to promote cleaner burning. This replaced MTBE.

Ethanol generates significantly less power than gasoline and 90/10 gasoline/ethanol blend will also yield slightly less gas mileage.
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Re: What octane gas do you use to fill your car?

Post by sambb »

Lets say your car is recommended to use premium fuel (Upper model lexus, BMW, mercedes)
Lets say you use regular 87 octane

What are the reliability consequences for the long term? None?
I understand that one may get a little performance decrease.
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Re: What octane gas do you use to fill your car?

Post by Quickfoot »

The price difference is 10%, but the mpg improvement is better than 15%. Is this related to warmer weather? Should I switch to 91 forever
This is a causation by correlation fallacy, the higher octane is not the only variable so it is not possible to attribute better fuel economy to higher octane especially given that higher octane often yields lower or at beast equal fuel economy.

What is most likely is you got gas without any ethanol in it and it is nearing summer so your car is running more efficiently. You'll notice most pumps now say "May contain up to 10% ethanol." 10% ethanol blends generally decrease fuel economy by 7% and E85 is 15% less.

Changing your air filter, properly inflating tires, and getting new spark plugs can improve fuel efficiency 10-15% as well so if you've done any of that (or got an oil change where they inflated your tires) recently those could also be a factor.
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Re: What octane gas do you use to fill your car?

Post by Quickfoot »

What are the reliability consequences for the long term? None?
Engine knocking and voiding the powertrain warranty to start with? If you are leasing and cause powertrain damage by using incorrect fuel they may come after you for the repair cost. Also if powertrain damage occurs for other reasons but they suspect or can prove you used incorrect fuel they can come after you for that damage because you may have caused or contributed to the damage.

If you want to save $0.10 to $0.20 a gallon go to a cheaper gas station or don't get a car that requires higher octane gas (higher octane cars are usually also more expensive than cars that run on regular anyway).
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Epsilon Delta
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Re: What octane gas do you use to fill your car?

Post by Epsilon Delta »

sambb wrote:Lets say your car is recommended to use premium fuel (Upper model lexus, BMW, mercedes)
Lets say you use regular 87 octane

What are the reliability consequences for the long term? None?
I understand that one may get a little performance decrease.
RTFM. It will have the details for the particular engine. I could generalize from my experience with a carburetor and manual choke, but it would be misleading.

Note that there is generally a difference between high octane being recommended and high octane being required. Recommended usually means using 87 octane will lose a little bit of performance. Required usually means using 87 octane will lose little bits of the engine.
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xzhou
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Re: What octane gas do you use to fill your car?

Post by xzhou »

Angelus359 wrote:That's a fluke.

Higher octane, in a car designed for 87, actually will give you worse fuel efficiency, with no additional power. Octane rating is just resistant to pre-mature detonation. Higher octane fuels allow for higher compression ratios. If your car doesn't have that higher compression ratio, it does nothing but slow down the burn speed, which reduces power output and fuel efficiency.

It's probably the warmer weather.
Thank you Angelus359 and others who questioned the gas mileage premium. It turned out to be more embarrassing than a fluke. I paid more attention this morning, and realized that I was looking at MPH, not MPG. Once I push the DISP button to the right type, it shows the same gas mileage as when I was using 87. Mystery solved, and one more data point on "no mileage difference between regular and premium".
I will edit the original post so that I am not misleading more people. On the upside, I just learned, again, that it is so easy to be happy in life if I am just willing to fool myself.
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Re: What octane gas do you use to fill your car?

Post by Ged »

I have an Acura. The user manual says it's ok to use regular occasionally, but if you use it long term it could lead to engine damage. I normally use 93.
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Re: What octane gas do you use to fill your car?

Post by Flobes »

FWIW Here in Colorado our octane needs and sales are adjusted for altitude. We choose from 85 - 87 - 91.

My Honda CRV runs happily on Regular, which is 85. Honda dealership and my mechanic both advised against using higher octane fuel, as it wastes money and may actually cause harm.

Alas, I am excluded from answering this poll for flatlanders.
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Re: What octane gas do you use to fill your car?

Post by Khanmots »

sambb wrote:What are the reliability consequences for the long term? None?
I understand that one may get a little performance decrease.
Octane measurement is a way of measuring how hard it is to cause ignition. Higher octane and it's harder.

This is important because the inside of your engine is quite hot... and as the air fuel mixture is compressed (prior to spark plug firing) it gets even hotter. If you're using a lower octane rating than the engine is built for then you get spontaneous combustion before the spark plug fires it off. This means that your piston is in the wrong place (trying to compress an explosion...) among other things.

My understanding is that older cars that used the wrong gas could have their engines die before too long from this. Newer cars have an anti ping sensor that will detect these early explosions and start dialing things back to try to prevent them. This is seen as a loss of performance... however, some do happen and so some damage to the engine does result. Over enough time (as the system will keep backing off trying to see if you've started using the right gas...) it can cause enough cumulative damage to be a problem.
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munemaker
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Re: What octane gas do you use to fill your car?

Post by munemaker »

jasc15 wrote:Why the aversion to ethanol?
Lower energy content (i.e. less gas mileage) and corrosive. Especially bad for older vehicles, some motorcycles and small engines.
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Re: What octane gas do you use to fill your car?

Post by tomd37 »

Munemaker,
What is an older car in your opinion. Many of the lawn mowing services around my area use one of the two PURE brand gasoline stations around here that sell 100% pure gasoline (no ethanol added) for their small engine equipment.
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Re: What octane gas do you use to fill your car?

Post by barnaclebob »

I think at one point the Ford Expedition manual said to use regular gas while the Cadillac Escalade said to use premium. Pretty sure they had the exact same engine at the time...
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Re: What octane gas do you use to fill your car?

Post by jasc15 »

barnaclebob wrote:I think at one point the Ford Expedition manual said to use regular gas while the Cadillac Escalade said to use premium. Pretty sure they had the exact same engine at the time...
It seems that every luxury car "requires" premium gas. A former coworker bought an Infiniti G35 (essentially a Nissan Altima) and was concerned about using the proper octane.
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Re: What octane gas do you use to fill your car?

Post by mike143 »

barnaclebob wrote:I think at one point the Ford Expedition manual said to use regular gas while the Cadillac Escalade said to use premium. Pretty sure they had the exact same engine at the time...
They maybe the same engine type but the luxury models usually have higher compression, more power, etc which requires premium fuel. This is similar to the Honda/Acura K series engines, they are about 160hp and require regular fuel in Honda vehicles and they are 200hp and require premium fuel in Acura vehicles.

Engine design dictates octane rating. It's not hey you have a luxury vehicle you need luxury fuel.

reddit.com: How can a modern car engine have a compression ratio of 11.5 to 1, and still run on 87 octane gasoline?

Ethanol blended fuels is some bad stuff. We already lost some small equipment to it. You cut pure gas with 10% ethanol you will get about 10% worse gas mileage. Almost like cutting your fuel with water. I can get pure gas in town but the price increase doesn't make up for the loss in mpgs.

http://pure-gas.org/
Last edited by mike143 on Mon Jun 16, 2014 3:19 pm, edited 2 times in total.
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Re: What octane gas do you use to fill your car?

Post by pyld76 »

jasc15 wrote:Why the aversion to ethanol?
Lower energy content for a given gallon of "gas," horribly destructive to small engines, corrosive if it sits in a gas tank for any length of time, and the way it is produced in North America is incredibly wasteful (relative to it's production in, say, South America).

Other than that, it's great.

E0 vs E10 will make a much bigger difference in mileage than running a car on 93 octane which only requires 87. I run what the manufacturer recommends.
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Re: What octane gas do you use to fill your car?

Post by placeholder »

barnaclebob wrote:I think at one point the Ford Expedition manual said to use regular gas while the Cadillac Escalade said to use premium. Pretty sure they had the exact same engine at the time...
Seems unlikely with them being from different manufacturers (Caddy is a GM product).
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Re: What octane gas do you use to fill your car?

Post by mike143 »

placeholder wrote:
barnaclebob wrote:I think at one point the Ford Expedition manual said to use regular gas while the Cadillac Escalade said to use premium. Pretty sure they had the exact same engine at the time...
Seems unlikely with them being from different manufacturers (Caddy is a GM product).
I didn't catch that. I thought they were comparing the same manufacturer (Suburban/Escalade).
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Re: What octane gas do you use to fill your car?

Post by Toons »

87- Honda Fit,Crv :happy
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Re: What octane gas do you use to fill your car?

Post by Ged »

Khanmots wrote: This is important because the inside of your engine is quite hot... and as the air fuel mixture is compressed (prior to spark plug firing) it gets even hotter. If you're using a lower octane rating than the engine is built for then you get spontaneous combustion before the spark plug fires it off. This means that your piston is in the wrong place (trying to compress an explosion...) among other things.

My understanding is that older cars that used the wrong gas could have their engines die before too long from this. Newer cars have an anti ping sensor that will detect these early explosions and start dialing things back to try to prevent them. This is seen as a loss of performance... however, some do happen and so some damage to the engine does result. Over enough time (as the system will keep backing off trying to see if you've started using the right gas...) it can cause enough cumulative damage to be a problem.
My Toyota Solara V6 (currently being used by my son) which is supposed to be fed premium gas for best results has a mechanism to adjust the timing if it detects pre-detonation. It's apparently working quite well as the car is 13 years old with 140K miles and has had no engine issues despite being fed off-brand 87 octane the vast majority of it's life so far.
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Re: What octane gas do you use to fill your car?

Post by Alex Frakt »

Here's something I posted on a previous thread on this topic.

Here's some excerpts from a USA Today article on the subject.
"I personally use regular even though my owner's manual says you'll get better performance with premium," says Lewis Gibbs, consulting engineer and 45-year veteran at Chevron oil company. He's chairman of Technical Committee 7 on Fuels, part of the Society of Automotive Engineers (SAE) Fuels & Lubricants Council. Gibbs knows gas....

The main advantage of premium-grade gas is that it allows automakers to advertise a few more horsepower by designing and tuning engines to take advantage of premium's anti-knock properties. But auto engineers generally agree that if you use regular in a premium engine, the power loss is so slight, most drivers can't tell.

"I go back and forth, and I'm hard-pressed to notice" whether there's regular or premium in the tank, says Jeff Jetter, principal chemist at Honda Research and Development Americas. He drives an Acura designed for premium.

Import brands, especially, use premium fuel to distinguish their upmarket models. Most Toyotas, for instance, are designed to run on regular or midgrade, while the automaker's Lexus luxury brand prefers premium. Same with Honda and its Acura luxury line....

The only modern engines that should really need premium are those with superchargers, which force-feed fuel into the cylinders. "You're driving along and just tramp the gas and the knock sensor cannot sense the knock fast enough in some cases," because the supercharger boosts pressure so fast, says Bob Furey, chemist and fuels specialist at General Motors.

Burning regular when the owner's manual specifies premium won't void the warranty, nor damage the engine, even the most finicky automakers say. "You're giving up perhaps just a little bit of performance that a customer wouldn't really even notice, it's so slight," says Furey....

All Porsche engines are designed for premium, too, but it's not available everywhere. "Our cars must be able to drive all over the world, and so we are able to run on regular," says Jakob Neusser, director of powertrain development at Porsche's research and development center in Weissach, Germany. "You don't have to feel that a mechanical problem or anything else will happen" using regular gas, even in the highest-performance, regular-production Porsches.
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Re: What octane gas do you use to fill your car?

Post by White Coat Investor »

Poll broken. We use 85 around here. I put 91 in the boat though. Seems to run better. Always put fuel conditioner in there too.
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Re: What octane gas do you use to fill your car?

Post by supton »

I've thought of experimenting in mine, running higher octane. I mean, if the fuel cost per mile goes down, more than the additional cost of premium, then it's a win. But driving plain jane Toyota's and reading various forums indicate few have noticed a bump--and I generally don't drive hard enough anyhow. Last I knew, in order to bump octane they had to use stuff with lower BTU's per gallon (stuff being other hydrocarbon chains found in gasoline, or additives, like lead, MTBE or ethanol). A higher compression engine could yield more mpg, but most are not aiming for mpg's. And when driven lightly it's doubtful that cylinder pressures are anywhere near where the extra octane is needed. Wild guess says that recent high perf cars won't care about low octane gas if you keep your foot out of it.

Due to federal regulations about evaporative emissions, summer gas has to have lower volatility. So the lighter aromatics get saved up for winter, and blended back in. Which isn't a bad thing, at least not for us Northerners, where extra volatility at -20F is a good thing. But go figure, winter gas has less BTU's than summer gas. Although a real killer is simply cold start, and longer warm up times. And lower tire pressures, if you don't keep an eye on the tires.

So, 87 in my Toyota's, and the good stuff for my Jetta: diesel! Which has a pretty low octane, yet yields some great mpg's...
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munemaker
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Re: What octane gas do you use to fill your car?

Post by munemaker »

jasc15 wrote:
barnaclebob wrote:I think at one point the Ford Expedition manual said to use regular gas while the Cadillac Escalade said to use premium. Pretty sure they had the exact same engine at the time...
It seems that every luxury car "requires" premium gas. A former coworker bought an Infiniti G35 (essentially a Nissan Altima) and was concerned about using the proper octane.
The thinking is...you buy a luxury car, you can also afford the higher insurance costs and premium fuel. Engines are more highly tuned for better performance. Why pay for a luxury car and then cheap out on the fuel?
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Re: What octane gas do you use to fill your car?

Post by barnaclebob »

mike143 wrote:
placeholder wrote:
barnaclebob wrote:I think at one point the Ford Expedition manual said to use regular gas while the Cadillac Escalade said to use premium. Pretty sure they had the exact same engine at the time...
Seems unlikely with them being from different manufacturers (Caddy is a GM product).
I didn't catch that. I thought they were comparing the same manufacturer (Suburban/Escalade).
Maybe it was the Navigator then. I just remember a friends parents talking about it when they bought their Expedition.

Edit: Just checked the manual for both the 2005 Navigator and 2005 Expedition. Navigator recommends 91 octane and Expedition 87 octane. The Expedition had the same engines on offer as the navigator, same HP.
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Re: What octane gas do you use to fill your car?

Post by Khanmots »

Ged wrote:My Toyota Solara V6 (currently being used by my son) which is supposed to be fed premium gas for best results has a mechanism to adjust the timing if it detects pre-detonation. It's apparently working quite well as the car is 13 years old with 140K miles and has had no engine issues despite being fed off-brand 87 octane the vast majority of it's life so far.
Which is why I differentiated between older and newer cars. However, pre-detonation has to occur for the sensors to pick it up. I'd bet some solid money that if you disassembled your engine and examined the inside of the cylinders and the piston heads that you have some damage.

With a modern engine with a working anti-knock sensor, how long will it take to cause a failure? Dunno. Might not happen in the lifetime of the car... anti-knock sensors probably prevent burn-through hotspots from developing. But there's still going to be some damage occurring. Wouldn't be surprised if the piston seals eventually go. You've been gambling and so far your gamble has paid off... however it's not one I'd care to take.
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Re: What octane gas do you use to fill your car?

Post by Alex Frakt »

Khanmots wrote:Which is why I differentiated between older and newer cars. However, pre-detonation has to occur for the sensors to pick it up. I'd bet some solid money that if you disassembled your engine and examined the inside of the cylinders and the piston heads that you have some damage.

With a modern engine with a working anti-knock sensor, how long will it take to cause a failure? Dunno. Might not happen in the lifetime of the car... anti-knock sensors probably prevent burn-through hotspots from developing. But there's still going to be some damage occurring. Wouldn't be surprised if the piston seals eventually go. You've been gambling and so far your gamble has paid off... however it's not one I'd care to take.
Do you have a basis for this claim? Look again at the article I quoted above. I think I'll trust the opinion of the "chairman of Technical Committee 7 on Fuels, part of the Society of Automotive Engineers (SAE) Fuels & Lubricants Council", "director of powertrain development at Porsche's research and development center in Weissach, Germany", " chemist and fuels specialist at General Motors", and "principal chemist at Honda Research and Development Americas" that it is safe to use regular even where premium is specified in non-supercharged modern cars.
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Re: What octane gas do you use to fill your car?

Post by BigOil »

Alex Frakt wrote:Here's something I posted on a previous thread on this topic.

Here's some excerpts from a USA Today article on the subject.
"I personally use regular even though my owner's manual says you'll get better performance with premium," says Lewis Gibbs, consulting engineer and 45-year veteran at Chevron oil company. He's chairman of Technical Committee 7 on Fuels, part of the Society of Automotive Engineers (SAE) Fuels & Lubricants Council. Gibbs knows gas....

The main advantage of premium-grade gas is that it allows automakers to advertise a few more horsepower by designing and tuning engines to take advantage of premium's anti-knock properties. But auto engineers generally agree that if you use regular in a premium engine, the power loss is so slight, most drivers can't tell.

"I go back and forth, and I'm hard-pressed to notice" whether there's regular or premium in the tank, says Jeff Jetter, principal chemist at Honda Research and Development Americas. He drives an Acura designed for premium.

Import brands, especially, use premium fuel to distinguish their upmarket models. Most Toyotas, for instance, are designed to run on regular or midgrade, while the automaker's Lexus luxury brand prefers premium. Same with Honda and its Acura luxury line....

The only modern engines that should really need premium are those with superchargers, which force-feed fuel into the cylinders. "You're driving along and just tramp the gas and the knock sensor cannot sense the knock fast enough in some cases," because the supercharger boosts pressure so fast, says Bob Furey, chemist and fuels specialist at General Motors.

Burning regular when the owner's manual specifies premium won't void the warranty, nor damage the engine, even the most finicky automakers say. "You're giving up perhaps just a little bit of performance that a customer wouldn't really even notice, it's so slight," says Furey....

All Porsche engines are designed for premium, too, but it's not available everywhere. "Our cars must be able to drive all over the world, and so we are able to run on regular," says Jakob Neusser, director of powertrain development at Porsche's research and development center in Weissach, Germany. "You don't have to feel that a mechanical problem or anything else will happen" using regular gas, even in the highest-performance, regular-production Porsches.

Alex is spot on. Bottom-line do what the owners manual says with all maintenance activities. You should only do what the Dealer says in any aspect of your vehicle's maintenance --- if it varies from the owners manualt -- if they can back it up with the technical service bulletin. Dealers are not engineers. Dealers often tell stories to increase margins. No engineer or or car company attorney would ever take the risk of a recommendation that produced ongoing damage to their product and brand. We worked with all car companies... They are extremely conservative when it comes to warranty & engines. This is not a misunderstood area of science.

Lewis Gibbs is truly an expert. My username is a clue. I spend entire career in downstream as well.

The available gasoline octane rating varies by geographic area primarily. Before the days of computer control, cars required slightly more or less octane on average based on altitude. There were also some to historic manufacturing reasons in some areas.

Gasolines are differentiated on additive packages. The base fuels is fungible in virtually all distributive areas today. Decades ago this was not 100% true-- it is now. Some brands are in fact cleaner than others i.e. to clean or leave less deposits. Some cars are sensitive to this some are not. Consumers associated premium with quality. Terminals do put transmix --- the mixed hydrocarbon interface in the pipeline between gasoline and diesel fuel or jet, in the regular gas but it is only trace amounts. Otherwise gasoline grades are generally the same except for hydrocarbon mix to get Octane rating up.

There can in fact be slightly more energy in regular gas, but I do not believe you can see this. Fuel economy testing is very difficult to do accurately, it virtually impossible for a consumer to really get a handle small differences --- in spite of what they believe.

Interestingly, decades ago, we did pat ourselves on the back for selling more premium. Is more profitable. It is also disingenuous to sell it goes to sell it to those who do not require it based on manufacturers recommend. So this has fallen out of favor. We've found it difficult to promote premium as a result. All the better ideas were killed by lawyers!

Amoco Ultimate was the market leader in selling premium. BP essentially killed off this brand. It was the benchmark.

Finally, ethanol is essentially a totally political question today. It does reduce fuel consumption and has damaged older small engines that we're not designed for it. As an engineer, it does not make modern cars burned clearer with oxygenates - ethanol or MTBE. Because the computer oxygen sensor essentially enables stoichiometric combustion (no unburned hydrocarbons) & the catalyst cleaning up any boo-boo during warm-up or transient response. Which are very small emissions in the first place. The arguments for ethanol are around energy independence, farming lobby, farming states and the not insubstantial feel-good properties of using it. This is not a political judgment. It's just an engineering fact. Ethanol only benefits modern small engines without computers, and older vehicles. I think this is a very small number. It has amazing inertia! My understanding is the energy balance for producing ethanol is about neutral. I'm not an expert on this.
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Re: What octane gas do you use to fill your car?

Post by BolderBoy »

sambb wrote:Lets say your car is recommended to use premium fuel (Upper model lexus, BMW, mercedes)
Lets say you use regular 87 octane

What are the reliability consequences for the long term? None?
I understand that one may get a little performance decrease.
My Benz has 66k on it, 8+ years old, has never seen > 87 octane gas and no troubles. But I live at >5000 feet and they say that makes a difference, too.
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