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  #1  
Old 02-11-2009, 09:01 PM
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MPG got worse without ethanol!!

This is interesting - I switched to PURE gas, which has no ethanol in it. Running 93 octane gas, after two fill-ups with the PURE gas, my mileage has gone DOWN from 17.5 to 16.2.


Less mileage with NO ETHANOL??? How did that happen?


-tp




"'90 300SE gets 17.5 in mostly city driving, with a lead footed driving style. I also keep it in 3rd sometimes in town to keep the motor in the power band and to make deceleration without brakes possible. That's using 93 octane gas with 10% ethanol. I feel reasonably certain that I would be getting over 20 if I drove grandma style.

I just found a station that sells PURE gas (the brand and the description) no ethanol!

It'll be interesting to see if my mileage improves noticeably."
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Old 02-11-2009, 09:23 PM
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unless you are a chemists you dont know what you bought

we in my shop have a NHRA divisional super gas car its an alky injected motor and uses twice the amount of alky to gas, we can switch back and forth , do runs not on the same day but it happens -- weather makes us switch -

did you use a hydrometer to check the specific of the fuel before and after the switch ????????????

what were the EGT readings < sorry its a street car performance difference should have been felt as the motors torque goes up 10 / 15 percent, at the track alky is 3 tenths of a second faster in the cars ET -

my guess the octain was to high and the compression was to low and it was wasted out the tail pipe - jz
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  #3  
Old 02-11-2009, 09:49 PM
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I say screw octane ratings. I put 87 (cheapest) in both my BMW and MB and they run fine....that's all bullcrap this octane stuff...I have a friend who is a chemist and asked him what octane really is and he hipped to the goods......
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Old 02-11-2009, 11:31 PM
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No, I did not check the specific gravity of the different fuels. That would be a little bit odd to do at a filling station.

I trust the owners of the filling station. They are a mom and pop shop, and go out of their way to provide good service. It's one of the ONLY shops in town that still has full service!

I actually asked the owner about the lack of ethanol in the gas. She said "we'll keep buying until they won't let us". I believe her.

Cliffmac - I respectfully disagree with you about the triviality of octane ratings. Higher octane fuel burns slower, that's a fact. If an engine is timed for the slower burning fuel, you risk damage by giving it low octane, faster burning fuel. If it is timed for lower octane fuel, then you waste money and lose economy and power by running high octane. If your chemist pal didn't mention that, then perhaps polycyclic aromatic hydrocarbons aren't his specialty.

Johnjzjz - I think you might be on to something.... The car requires 91 octane gas. Perhaps the 93 octane PURE gas was in fact so much better than the BP stuff that my motor just couldn't burn it optimally. I just filled it up again today. If nothing changes MPG wise during my next fill up, I am gonna try a little experiment. I'm going to try 50/50 93 octane and 87. That should leave me with a 90 octane rating. Perhaps my MPG will re-appear?


-tp
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  #5  
Old 02-12-2009, 09:08 AM
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What's NOT said about etOH

Unless you're really digging for info about ethanol fuel, you are not really likely to find much where it matters IE: behind the wheel.

Ethanol does serve as a 'volume expander' for gasoline and it does increase octane ratings (lowers the likelihood of pre-ignition under compression.) Since etOH actually has a higher, 116, octane rating (depending on how it's tested.)

BUT, when mixed with gasoline and burned in a car engine tuned to burn gas, it lowers the BTU (overall heat generating capacity) of the given volume it's mixed in. The change in mileage can be accounted for somewhere, even though one might expect it to be the reverse.

CAVEAT: What any of us buy at any given gas station one day might not be the same the next day. Regardless if we buy at the same time, from the same pump. The pipeline/transport system carries all kinds of stuff and what comes out is seldom if ever identical over time.
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  #6  
Old 02-12-2009, 10:55 AM
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Quote:
Originally Posted by cliffmac View Post
I say screw octane ratings. I put 87 (cheapest) in both my BMW and MB and they run fine....that's all bullcrap this octane stuff...I have a friend who is a chemist and asked him what octane really is and he hipped to the goods......
Very foolish comment and if your friend is a chemist he would know that an internal combustion engine designed to run on a specific octane number needs to do so to avoid pre-ignition/detonation/pinging/pinking whatever you want to call it !!
This can be damaging to an engine.

It depends on what you drive and the compression ratio and if the engine management employs knock sensors that retard the timing when too low of an octane rating is used.

The other thing to consider is that the higher octane tier one gasolines contain additives such as polyether amine to keep the fuel system clean.

The manufacturers know more then your chemist friend and there is no conspiracy to make one buy a higher octane then needed.
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Last edited by RBYCC; 02-12-2009 at 12:06 PM.
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  #7  
Old 02-12-2009, 12:00 PM
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Quote:
Originally Posted by cliffmac View Post
I say screw octane ratings. I put 87 (cheapest) in both my BMW and MB and they run fine....that's all bullcrap this octane stuff...I have a friend who is a chemist and asked him what octane really is and he hipped to the goods......

man I hope I never get one of your used Mercedes
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  #8  
Old 02-12-2009, 04:05 PM
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As might have been mentioned; Octane is a number indicating the burn rate of the fuel and it's resistance to detonation, and has nothing to do with the energy (BTU/h) of the fuel.

However, higher octane in higher compression engines will be able to burn more efficiently as the spark can be advanced further, allowing the engine to extract more of the energy from the same BTU/h of fuel.

So, octane doesn't mean more energy, but it can mean more power. Going higher than the car is able to utilize will do nothing however and at high altitudes high octane can actually be a disadvantage in a non-turbo engine.

As far as using an octane lower than the carmaker's specification: In the owner's manuals on my M104 cars it warns against using lower octane fuel, and has specific reduced speed and load requirements if lower octane fuel must be used. Mixing lower octane with higher octane is allowable to a certain percentage per the manual.

Using too low an octane can cause detonation, which can lead to burned valves and damaged pistons if the engine isn't designed to compensate enough. It also will cause the ignition timing to retard in most modern cars, which will lower the power output and efficiency, and increase tailpipe emissions.
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Old 02-12-2009, 05:23 PM
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I know you all were provoked into responding, so I can't fault you, but this was supposed to be a MPG versus Ethanol thread and not a "I run cheap gas in my expensive car" thread.
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Old 02-12-2009, 07:39 PM
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In that case:

Ethanol has less energy than gasoline, and will typically deliver lower fuel mileage. However, it also can have higher octane, which can allow your engine to burn it more efficiently, and return some of the loss of energy content in efficiency.
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Old 02-13-2009, 12:15 AM
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sorry, but octane doesn't mean anything unless you are driving to the max of the engine capacity. any octane will be just fine unless you are redlining the engine....it would matter then but who amoungst us redlines the engine? I don't, 87 vs 91? come on, that's trivial and the computer would compensate for that anyway....that's all tripe.....It's to make peope who drive BMWs and Mercedes and so forth think they have this really high performance engine that must have to have this fuel to make it perform up to these standards...pure hogwash....believe me, pure marketing. Not only that, but German octane is different than US ratings.....
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Old 02-13-2009, 12:31 AM
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Tell you what, my brother flies airplanes (Cesnas and little guys like that there)...I took him to Palwaukee Airport in Illinois to fly back to Minneapolis and he fueled the plane up with 103 octane aviation fuel and I snuck a half of tank of this non-taxed fuel into my BMW. All it did was make the engine run hotter, no performance increase at all, in a non-catalytic 1976 BMW 2002. That was my first clue as to the game.....it's all bull....has nothing to do with anything but ego, there are these things called knock sensors that will compensate for fuel value and they are calibrated for the lower octane fuel as a matter of course. MB and BMW and so forth expect you, as the average owner to not put premium in and have hence programmed the ECU for that. That's why if you 'chip' an ECU you MUST put premo in or that'll really screw things up. The car is dumbed down for the average driver/owner....it's true
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Old 02-13-2009, 09:36 AM
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Quote:
Originally Posted by cliffmac View Post
sorry, but octane doesn't mean anything unless you are driving to the max of the engine capacity. any octane will be just fine unless you are redlining the engine....it would matter then but who amoungst us redlines the engine? I don't, 87 vs 91? come on, that's trivial and the computer would compensate for that anyway....that's all tripe.....It's to make peope who drive BMWs and Mercedes and so forth think they have this really high performance engine that must have to have this fuel to make it perform up to these standards...pure hogwash....believe me, pure marketing. Not only that, but German octane is different than US ratings.....
You really don't have a clue...believe what you want.
Helps to wear a tin foil hat.
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  #14  
Old 02-13-2009, 11:25 AM
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Quote:
Originally Posted by cliffmac View Post
sorry, but octane doesn't mean anything unless you are driving to the max of the engine capacity.
There's no reason here to apologize in advance for prevarication. It is your inalienable right.
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  #15  
Old 02-13-2009, 05:13 PM
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Thanks for hijacking my thread, Cliffmac.

I was TRYING to get a discussion on ethanol versus mileage and instead we have drifted off into yet another case of you bashing of high-octane fuel.

Not only are most of your assertions incorrect, but they're irresponsible. Luckily there are plenty of people here to point out your folly lest somebody actually take a notion to follow your advice.

Plus, those "things called knock sensors" as you so eloquently put it only appear on newer cars. My '90 300SE doesn't have one, and I doubt the '79 BMW does either. In any case, the result of a detected knock is the computer retarding ignition timing in order to curb the detonation. In order for it to work, you have to make your car detonate first! In other words, all it does is try to stop damage all ready in progress. If that concept makes you happy running low octane fuel, then cheers!

I dare you to DOCUMENT the fuel you've been running and present it when you try to sell the car.

Normally I don't like to go off on other contributers here, but you've stolen my thread and filled it with off-topic disinformation.

If you really like to flame bait, start a thread of your own. Last time I looked it was free.

"MB and BMW and so forth expect you, as the average owner to not put premium in ....."

Right. That's why it says PREMIUM FUEL ONLY on the instrument cluster. You're a genius.


-tp
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