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Higher compression engines are more fuel efficient. Some modern turbocharged cars require premium fuel. The trade-off for higher priced fuel is better fuel efficiency. If the engine was designed to burn 87 octane, buy 87 octane.
It's not really relevant, but ethanol is an anti-knock additive. E10 fuel lets the distillers use cheaper fuel fractions, keeping fuel costs down for everyone. The trade off with ethanol is less energy per molecule (not enough carbon) which reduces mileage. It's all a juggling act.
A friend just posted a picture in Facebook of a gas pump where the listed price were $3.95, $3.98, and $3.99.
This brought up a question I sometimes wonder about: is there ever a time when the price differential is so low that it makes sense to buy premium gas?
No.
If your car is designed to run on regular, buy regular. There's no advantage to spending any more money on higher octane.
It's a different story if you have a performance car that is designed to run on premium (like my Viper). Then you are stuck paying the higher price no matter how high it gets.
Only if your car requires it - otherwise it's a waste of money.
Quote:
Originally Posted by adjusterjack
No.
If your car is designed to run on regular, buy regular. There's no advantage to spending any more money on higher octane....
Etc., etc., etc.... I think everyone so far has basically said this, and for the past 50 years I've also been saying it. BUT, I've been wondering lately.
The stations where I usually buy fuel serve up the premium (highest octane) gasoline with NO ethanol. Lower octane fuels normally have 10% to 15% ethanol (much higher with E85, of course). I'm not sure about the energy (btu?) of gasoline vs. ethanol, but I've read that a gallon of ethanol provides about 60% of what a gallon of gasoline does, and that adding 10% ethanol to gasoline reduces its energy by about 3%. Therefore, I'd think if premium (with no ethanol added) was priced only a percent above regular (with ethanol added), it would be cheaper per mile.
WHILE ON THE SUBJECT:
The ONE time I tried E-85 in my car, the fuel efficiency was cut by about 35%. The engine light also came on, and it stayed on until I'd refilled a time or two to get rid of that nasty E-85. And before you ask, yes, my car was supposedly designed to run on E85 (flex-fuel).
I switched to the premium (ethanol-free) gasoline for my lawn mower a year or two ago. Lawn mower sat outside all winter, from late October until late April (6 months), with temps well below zero much of that time, and it started on the very first pull this spring -- and that was shortly after I'd torn a rotator cuff in my right (pulling) shoulder. I might have been able to do that with gasoline+ethanol with enough gas treatment added to it, but it's easier to just buy 5 gallons of ethanol-free fuel every summer.
The two places you can always find ethanol-free fuel are marinas and airports. In rural areas, there is always a place to buy ethanol-free premium for chainsaws.
I ran 100 oct last summer with my turbo Cayenne with tune, etc... throttle response was very noticeable, but at $8.50 a gallon (I was damn near empty when I bought) ten gallons was enough. Wasn’t really worth the $85 I spent unless you were going to a track. Every vehicle I’ve had requires premium for last 15 years.
I have seen cars that were designed for regular that ran noticeably better on premium or mid-grade (which is typically a 50-50 blend of regular and premium). My old Subaru pings on regular, particularly in summer with the A/C on. Sometimes, tolerances stack up to give a bit more compression than nominal. Frequently, with age, carbon buildup on piston heads will give an increased compression effect.
Older cars where you can adjust the timing manually, given the OP's posted price differences, you would probably be money ahead to advance the timing a few degrees and use premium.
Anymore around here the most commonly available ethanol free fuel is Conoco 91 octane, so most of my old rigs, I have turned the advance up a bit from what the book says, and I run that.
If you log your mileage, maybe try a tank full or 3 of premium, see if you get any better mileage. The book says what it says, but you can measure what your car does in real life.
Ditto to all the above. It doesn't help, unless your engine can vary it's timing to capitalize on the higher octane. Mine will, but after measuring a few tanks the improvement doesn't cover the cost spread between premium and regular.
As a first time DI engine owner, I've done quite a bit of reading on preventing the valve deposits and oil dilution with fuel that are associated with these engine. Higher compression DI fuel maps are often programmed to run slightly rich with regular fuel to prevent pre-ignition. I've read where people have dropped their fuel dilution numbers (measured by UOA) by switching to a premium gasoline. The fuel mapping and timing changes, allowing the engine to run leaner and more efficiently. So in this case, premium can be better - but not because of mileage or hp gains. So far, I haven't been diligent enough to run only regular on one OCI and premium on the next to see if it actually impacts my fuel dilution numbers on an OCI. But maybe some day.
I'll also note this is only true if you have a higher compression DI engine that is able to monitor and change timing on the fly. If you have a 1992 Ford Escort, than no...this doesn't apply to you.
The ONE time I tried E-85 in my car, the fuel efficiency was cut by about 35%. The engine light also came on, and it stayed on until I'd refilled a time or two to get rid of that nasty E-85. And before you ask, yes, my car was supposedly designed to run on E85 (flex-fuel).
I switched to the premium (ethanol-free) gasoline for my lawn mower a year or two ago. Lawn mower sat outside all winter, from late October until late April (6 months), with temps well below zero much of that time, and it started on the very first pull this spring -- and that was shortly after I'd torn a rotator cuff in my right (pulling) shoulder. I might have been able to do that with gasoline+ethanol with enough gas treatment added to it, but it's easier to just buy 5 gallons of ethanol-free fuel every summer.
This makes no sense. The easiest way to increase octane rating is to add ethanol so your higher-grade fuels are MORE likely to have ethanol, not less. A true E85 blend is about 105 octane. Combine that rating with ethanol's superior cooling characteristics and you have an effective rating of around 110 octane. Thus you can run up a to 15:1 compression ratio on E85 without blowing holes in your pistons. That's why "flex-fuel" vehicles get such crappy fuel economy on E85 -- they have to use a compression ratio low enough to accommodate fuel all the way down to 87 octane so they can't take advantage of E85's superior detonation resistance.
The ONE time I tried E-85 in my car, the fuel efficiency was cut by about 35%.
That's because ethanol has a lower energy content than gasoline. The higher the ethanol content of fuel, the more fuel that must be burned (relative to normal gasoline) that must be burned in order to do the same amount of work. Thus, the claims about ethanol-blended gasoline beinf better for the environment are specious, at best. Also, alcohol tends to dry out the seals in an automotive fuel system.
And last but definitely not least, more fuel burned = more fuel taxe$ paid.
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