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  #1  
Old 08-30-2002, 07:43 PM
J.HIDALGO's Avatar
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Question Premium gas?

I noticed that lately, a lot of car companies are requiring Premium fuel in their engines i.e. nissan, vw, including MB, etc. This does not make sense to me since gas prices are slowly creeping up.
What ill long term effects are there for the engines if these vehicles are feed with reg/med gas other than affecting performance, engine timing retard, pinging, etc?
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  #2  
Old 08-30-2002, 08:04 PM
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Most higher octane gasoline formulations also contain a greater number of cleaning additives. These additives are as beneficial as the greater octane.

At an indie shop recently I had a chance to see a 3.0L M103 engine with the head off, and couldn't believe how clean the combustion chambers were. The car had 375K on the odo, and the chambers looked like new.

I asked the mechanic, and he said the reason was frequent oil changes allowing good sealing, as well as constant use of good quality premium gasoline.

"No Italian tune-up required here, eh?"
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  #3  
Old 08-30-2002, 08:15 PM
jfujimoto
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J.H.,

You're opening up a big can of worms with the gas octane/pricing issue.

Jeff
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  #4  
Old 08-30-2002, 09:10 PM
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fuel

As someone that has spent 20 years overseas (not in the military) and been through 80+ countries I can't believe that Americans, who, by any standard, have the cheapest energy costs in the world, complain about the cost of gas. Compared to the number or hours you have to work to buy a gallon of fuel or a thousand therms of natural gas, or a kilowatt of electricity, energy costs are way cheaper than they were in 1955. It is only the numbers that have changed. I remember in 1956 I was digging septic tanks with a pick and shovel in the S. Texas summer heat for $0.75 an hour. At thime I think that gas was about $0.25 a gallon. I saw it as low as $0.09 a gal. during price wars, but that doesn't count. That means that a gallon costs 1/3rd. of my hourly wage. Now I make $20. an hour and gas is $1.20. That means that instead of only getting 3 gals. per hour I can now get 16. Now, that is cheap fuel. A vacation driving around Europe will put gas prices in perspective. Not only are they 4+ time what they are here but the average working man makes about 2/3rds. of what we make here. And their taxes start at about 40%. Be happy for what you have.
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  #5  
Old 08-30-2002, 09:51 PM
Jackd
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There has been at least 500 posts on the gasoline issue on various forums.
There are a lot of misunderstandings, misconceptions, rumors on the real value of premium gasoline over regular and/or mid grade.
Which one to choose???
Maybe my 25 years experience with a major petroleum products refiners can be of help.
1) Engine manufacturers: They base their recommendations solely on the compression ratio of their engines vs. grades of gasoline available in the market they sell their cars. Generally, manufacturers recommendations are on the (very) safe side. Why would they risk having engine problems (warranty, image) by specifying a ''good enough'' gasoline grade. So, they tend to be very conservative and generally would require a bit more octane their engine realy need.
2) Petroleum companies: They will try to sell the highest volume/proportion of the premium type. They make more money on premium than on regular gasoline. Typical marketing approach. The higher priced, the better, they say....
3) Consumer: many feel that buying the most expensive will garanty the best buy. A $6,000. Cartier watch is certainly percieved as being better than a $10.00 Timex watch ( In terms of keeping/giving the exact time of day, Timex is probably as good as a Cartier). As consumers tend to be influenced by 1) Engine manufacturers and 2) petroleum company marketing campains, They are left with the impression that premium gasoline must certainly be superior than regular grade gasoline...... Not necessarily true for most applications. And those impressions are transmitted from one generation to the next.
Thruth: Premium gasoline differs from regular gasoline ONLY in their ability to resit pre-ignition (pinging). If any given car can run satisfactorily with regular grade gasoline, filling up with premium grade is a total waste of money. No more power, no more MPG,
Exception: On some newer cars, (not on a 300E) total timing dwell is retarded on the onset of pre-ignition. Retarded timing reduces power.
Some (only some) premium gasoline could contain a bit more of fuel system cleaning additive, which is not always required.
They best way to find out which gasoline your car prefer is firsts to go to a mid-grade if you have been running with premium. Open your ears, listen carefully for pigning/pre-ignition noise on acceleration. If you ear nothing bad, try regular gasoline and listen. No pigning? regular gas is for you.
That's unless you still want to give your money away to the big oil companies. Your choice.
JackD
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  #6  
Old 08-30-2002, 09:58 PM
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Kip and others,

I am not complaining about the cost of fuel here in the USA. I am also fortunate enough to have been overseas (not 80 countries thought) and I am very aware of the fuel prices around the world. As a matter of fact, diesel and natural gas are already an accepted reality in other countries. However, I am more interested in the mechanical aspect of the effects on an engine by using lower octane than required by the car makers.
The reason for my question? you may ask. Simple. I talked to a couple of salesmen in a small auto show. One for Nissan and one from VW (MB was not represented). The Nissan guy told me "you don't have to use premium gas, just stick with whatever gas you start with"... The VW guy told me "you can use regular (in a Jetta 1.8T) but you won't get the same performance as with premium"...
Sorry for the long post but, I think this will clarify my question a little bit. I hope!
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  #7  
Old 08-31-2002, 12:16 AM
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Interesting points ...

It used to be a pretty straightforward topic ... if your car was running properly and it pinged, you needed higher octane.

Then came EGR and other mechanical issues and problems led to pinging with the correct gasoline and some folks then simply went to the next grade up. Should have fixed problem.

Issue now I think is how flexible the entire engine is to changes related to fuel octanes ... if your engine management system is working properly, many engines will accept a broad range of octanes, but performance (power) will suffer ... questions, though are: 1. does the mileage also suffer, and if so, how much relative to the marginal decrease in the cost of the regular versus "designed for" octane; 2. is the engine, with timing retarded and other engine functions modified to prevent preignition, being damaged in any way?

Data on this would be very useful ... while I have seen a few articles on this in magazines, don't know if anyone has done a thorough test with various types of engine management systems to see which ones can adjust to lower octane, which ones do it better than others, and whether or not this is an OK thing to do, given the other factors.
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  #8  
Old 08-31-2002, 11:35 AM
hradek
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Octane

Octane = Primarily the level of anti-knocking additives added to fuel. The higher the number, the greater amount of this additive. Octane, according to the source, does not directly affect power or economy. Your engine, with its knock sensors and others, decides how to perform upon these readings.
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  #9  
Old 08-31-2002, 06:09 PM
Jackd
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Interesting questions Stevenson.
Some cars electronic systems (I don,t know about Mercedes) will also slightly enrichen the fuel/air ratio to combat pre-ignitionif retarding the final timing is not enough At this point, MPH wold decrease slightly.
An engine running with slightly retarded ignition will not be damaged, although very prolonged condition could possibly induce more deposits in the combustion chamber.
JackD
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  #10  
Old 09-03-2002, 11:29 AM
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I drove thru all of scandinavia recently, and there were only two grades of gasoline available there - regular and premium. Regular was 95 octane ((R+M)/2), premium was 98. All cars use one of these two.

So why are we cribbing/discussing using 93 octane in the US? It's lower than regular in a lot of countries (cost aside).

FWIW, as compression ratios are going up and tolerances down, the octane requirement in fuels has been steadily going up. Heck, 30 years ago, 83 octane was used very commonly. Why don't we discuss going back to 83 now? Another 10 years, and we'll accept 93 as "regular" and go on with life.
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  #11  
Old 09-03-2002, 02:24 PM
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Well, I certainly feel sorry for you Californians and other Westerners that are limited to 91 octane "oxygenated" unleaded fuel, during certain times of the year I believe.

On a driving trip over there recently, I clearly noticed a performance difference with 91 oxygenated in my 300E, versus the 93 octane you can get here in Texas ... not to mention the price difference. While I was there, super unleaded was about $1.88 a gallon ... here it averages about $1.48 or so. I dare to guess what performance the regular unleaded would've given me.

Now, I have no clue if the difference was due to the octane, or in the oxygenation, but the performance difference was definitely there. Climbing mountains, I also heard an occasional ping or two.

I'll have to side with BlackMercedes. You get what you pay for. I only use premium unleaded as stated just below my fuel gauge needle.
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  #12  
Old 09-03-2002, 02:29 PM
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In Canada, we get charged a HUGE price difference for premium gasoline. Most of the time, it's 10-12 cents per litre. That's about 40-50 cents per US gallon.

I drive the C230 lots. About 30,000 kilometers per year. I average 9.0L/100km combined driving, using about 2700 litres of fuel per year.

That $0.10 adds up to $270.00 per year in extra costs. Sounds like alot, but in the grand scheme of annual operating costs for a late-model Mercedes, it's chump change.
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  #13  
Old 09-03-2002, 11:06 PM
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On oxygenated gasoline: generally, the added oxygenates (ethanol?) have less BTUs per gal, thus provide less power than *pure* gasoline.
On the regular vs premium fuel: I have had many vehicles with varying compression ratios/performance engines. I have always tried to use the lowest octane fuel that will not allow pinging on a properly tuned engine in good condition. If 87 octane fuel doesn't allowing pinging, then that's what I use.
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  #14  
Old 09-04-2002, 01:29 AM
Gympie
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I'm in Colorado which the state requires the min. octane rating of unleaded fuel to be 81. As we are higher in elevation, the need for a min 84 octane is not needed. We pay the same amount (or more) for what lower elevation states pay for 84 octane. Also, the state requires a higher amount of ethenol to be used in our fuel.
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  #15  
Old 09-04-2002, 08:39 AM
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By coincidence, I spoke to some Ford engineers yesterday on this matter. By using premium fuel in todays vehicles, the manufacturer can get the best performance and emissions possible. Primarily, it's fuel mileage they are concerned with. The auto companies need to get the most mpg out of every vehicle they manufacture. If it means putting a sticker that says "Premium Fuel Only", then it's a no-brainer.

Using a lower grade fuel will degrade performance slightly but whether it is econically better depends on the price you pay and the decrease in mpg. I would advise you use premium if you are towing though, since the engine will run cooler as the timing will be more advanced. All engine controllers that we design here have knock sensors in them so the engine won't ping regardless of the fuel you use.

I myself drove an ML320 1500 miles from Houston on Regular Unleaded this last weekend and averaged 23 mpg with nary a ping.
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