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Old 04-23-2011, 10:30 PM
 
Location: Victoria TX
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Quote:
Originally Posted by Asheville Native View Post

True some cars require premium. Why did someone buy it. Is it necessary for you daily commute or to get the groceries home from the store?

I can say the same thing about 90% of the features that are unnecessarily sold as bloatware on cars. My car has stick shift, crank windows, manual locks, two radio speakers (a spare if one breaks, I guess), mechanical locks, 98c keys, ratchet/lever seat adjustment, mirrors that you adjust by opening the window and grabbing them and twisting. Regular gas, 38 mpg, maybe 80 mph---never tried it.
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Old 05-04-2011, 05:53 AM
 
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Bottom line is if these high gas prices are a strain on your budget then its time to get out of the pickup truck or SUV and into something more economical,no problem finding cars on the market that get in the 40mpg range, also driving less can reduce costs.
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Old 05-04-2011, 10:14 AM
 
Location: Grosse Ile Michigan
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Quote:
Originally Posted by jambo101 View Post
Bottom line is if these high gas prices are a strain on your budget then its time to get out of the pickup truck or SUV and into something more economical,no problem finding cars on the market that get in the 40mpg range, also driving less can reduce costs.

Could you please point me in the direction of a seven passenger car that gets 40 MPG? Thank you.
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Old 05-04-2011, 10:33 AM
 
27,033 posts, read 38,285,206 times
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Quote:
Originally Posted by Asheville Native View Post
Marketing to idiots. Many people driving cars that will run fine on regular have been sold on the lie by oil companies that "premium is better". Like they say, a fool and his money are soon parted.

True some cars require premium. Why did someone buy it. Is it necessary for you daily commute or to get the groceries home from the store?
Uh, because it's the car we wanted. The fuel required to run it is/was not a consideration. To me 20 cents a gallon is not much difference at the pump. For me that's about $4 every two weeks.

Our next new vehicle will be a high mileage one. We will be traveling a lot in retirement so it will become a consideration. However, I will not forgo comfort in order to spend less on gasoline.
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Old 05-04-2011, 10:42 AM
 
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All of the different octane levels are based on petroleum. When the refinery "cracks" the crude oil they end up with different hydrocarbon chains. These chains are then separated into their composite groups and that is where different fuels come from. You end up with the following:

Methane - single carbon atom.
Propane - three atoms.
Butane - 4 atoms.
Pentane - 5 atoms.
Hexane - 6 atoms.
Heptane - 7 atoms.
Octane - 8 atoms.

The more atoms it has the more resistant it is to detonation under compression, so octane is the hydrocarbon strand with the most resistance to detonation. "87" contains 87% octane and 13% of another carbon chain, generally heptane. "93" contains 93% octane and 7% of another carbon chain, again generally heptane.

Different qualities of fuel contain varying amounts of these base chains. The best "light sweet" crude from the Middle East contains a lot of octane. The lower end stuff contains a lower amount of octane.

In WW2 they discovered that they could add TEL (tetraethyl lead) and boost the compression resistance of fuel. Using "leaded" fuel allowed refiners to take the lower quality material and use more of it in their mix, so they may have used a mix of 60% octane, 20% heptane, 20% pentane, added in TEL and got the equivalent of "87". Of course, lead is bad for the environment and it's use was eventually banned.

The replacement for TEL was MTBE, that provided the same effect (boosting octane), but wasn't as effective, requiring more octane chains per gallon, than when TEL was used. As we all know, MTBE is also a rather pervasive pollutant and it's use has dropped dramatically in the U.S.

Ethanol, has now largely replaced MTBE use, but again is less effective overall, requiring refineries to use even more octane chains to get the same level.

So, all fuel grades are 100% crude petroleum based (now each gallon is mixed with up to 10% ethanol, but the other 90% is all petroleum fuel). The main component in gasoline is octane carbon chains. This is most prevalent in "good" crude. So, higher octane gas always required more of the "good" octane chains, hence the price difference. As supplies of "good" easily refinable oil drop, the cost of octane goes up.

The banning of all compounds that easily boosted compression resistance do to their environmental impact has meant that premium fuels are now solely reliant on the octane chains to get their rating.

Edit: Wanted to add something on pricing. Say, regular was $1 and premium was $1.05, that represents a 5% difference. If regular than goes to $4, that same 5% difference would mean that premium is now $4.20. Add in more plentiful and hence cheaper filler carbon strains that make up a larger portion of regular and you can easily add another few cents to the price difference.

Last edited by NJGOAT; 05-04-2011 at 11:02 AM..
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Old 05-04-2011, 11:28 AM
 
22,770 posts, read 25,283,115 times
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Quote:
Originally Posted by jtur88 View Post
I've tried googling this, but not coming away with a very clear answer.

Why does the differential between premium and regular rise in proporation to oil prices?

I have long thought that premium is basically regular with non-petroleum octane-boosting additives, and those additives ought not be influenced by crude prices. But that may not be the case.

It seems that premium is a blend of regular low-octane gas and a special high octane carburetant, which also comes from the same petroleum, is cracked differently, but still goes up and down with crude prices.

Can someone clarify this?

20 years ago, when Georgia gas was 78c a gallon [sigh], the premium grade was only about 5c more. But now at my local station, premium is 37c more than regular.
to me it would make more sense to measure the differential in relative terms -- expressed as a percentage -- rather than absolute terms like you are doing.
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Old 05-04-2011, 11:44 AM
 
Location: Northern MN
3,869 posts, read 12,557,633 times
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90% is a reach.
Fuel, 100% crude petroleum after refining, also needs a package add to it for lubrication, cleaning agents and oxygenates.

Some octane levels are increased from adding additives to the fuel.

Quote:
Originally Posted by NJGOAT View Post
So, all fuel grades are 100% crude petroleum based (now each gallon is mixed with up to 10% ethanol, but the other 90% is all petroleum fuel). .
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Old 05-04-2011, 12:15 PM
 
14,777 posts, read 34,647,129 times
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Quote:
Originally Posted by snofarmer View Post
90% is a reach.
Fuel, 100% crude petroleum after refining, also needs a package add to it for lubrication, cleaning agents and oxygenates.

Some octane levels are increased from adding additives to the fuel.
You are correct, my example was a generalization of what goes into it. The OP was questioning the petroleum content of premium vs. regular. Overall, the additives amount to a very small percentage of a gallon, while the mix of hydrocarbon chains used and their modifiers also vary greatly based on the feedstock used. The additives are also generally hydrocarbon/fossil fuel based elements that contain large amounts of oxygenating compounds. For instance MTBE was a by-product of natural gas refining. Many current additives are butane based.
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Old 05-04-2011, 12:40 PM
 
33,203 posts, read 39,291,585 times
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Quote:
Originally Posted by Coldjensens View Post
Could you please point me in the direction of a seven passenger car that gets 40 MPG? Thank you.
If every time you go out you have to drag along 7 people i'd think about incorporating yourself as a transportation company buy a bus and make the expenses a tax write off..
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Old 05-04-2011, 07:27 PM
 
Location: Eastern Washington
13,435 posts, read 42,908,992 times
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Actually, at least around here, since gas was about $1/gallon, premium has cost about $0.20 more per gallon than regular. Now that it's getting up around $4, the spread is a little more.

On many cars, you actually get a better cost per mile with premium. Our Subaru is like that, particularly in summer, when with the A/C on it tends to ping a bit on regular. As Sunsprit has pointed out, probably I need to replace the knock sensor (although even then it may still get enough better MPG to justify the premium, the knock sensor just retards the timing).

On older cars like 60's to 80's Detroit Iron, you can almost always crank on a bit more total advance and get better mileage with premium, to the point the cost per mile is less than with regular.

Newer cars that are designed for premium *can* generally use regular with no problems, again knock sensors retard the spark to stop any detonation - for freeway cruising in cool weather you *may* come out a bit ahead, but not much.

Some cars tend to build up carbon in the combustion chamber more than others, in some cases this leads to increased octane demand as the car ages. On the other hand the old 8V VW motors of the 80's will cheerfully run on regular gas and would probably work OK on the sub-regular you see on sale in some European countries and Russia (about 70 octane)

Thumb rules are just that, and no substitute for actually knowing the technology you are working with, this seems to be too much to ask of the Great American Motoring Doofus, but it's true just the same.
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