gas mileage enigma

[raulcruz01@earthlink.net]

So I've been reading some of these threads on gas mileage and haven't found an answer to MY mystery... Erratic, inconsistent gas mileage.

 

96 obw, 136k, recent tune up with new pcv valve, plugs, wires, fuel filter, oil change with 5w30 valvoline high mileage oil, checked tire pressure, o2 sensor changed about 20k ago or so ago.

 

In town, in the teens (17mpg or so) consistently. On the highway, anywhere from 24-28. This week, I filled up and went all highway miles. My friend drove my car for about 50 or so miles and drove it like Mario Andretti - screaming rpm's on each gear. I was ready to take the wheel and thought for sure he'd kill my mileage. That's when I got 28. Filled it up and did about 100 miles on the highway, winds at about 55 mph on I-80 in wyoming. I could tell I was getting less because the needle was dropping quicker. Drove it conservatively and got 18 or 19.

 

What's the deal??!! I purposely didn't get a full sized SUV because I thought I'd be doing better on mileage. It's even a 5-speed! Am I missing something.

[raulcruz01@earthlink.net]

By the way, I also put in a whole bottle of Seafoam three tankfulls ago.

[tunered]

i think the gasoline we are getting is so inconsisent there is no way to get a accurate milage,mine does this too and ive heard other stories of the same. i quit worring about it and just put some in when i need to.

[Chef]

Sounds to me like you might be leaking gas. Check your lines out, and aroudn the fuel tank.

[daehttub2000]

You will get odd mpg results on a single tank.

 

If you're really serious about getting a true mpg:

 

You need to average your mileage over several tankfuls. It helps to stick to the same gas station and pump and let the tank go down all the way before filling it up. The auto cut-off at the pump can really vary depending on the station, temp, etc. There is also a thread about 10% ethanol gas that explains some of the possible mpg variance.

 

You can get a bad highway mpg if you run into headwinds (you said 55mph winds???), go significantly over 65mph, or have a loaded car.

 

I wouldn't worry too much if you just got one bad mpg reading. It happens.

[nipper]

You will get odd mpg results on a single tank.

 

If you're really serious about getting a true mpg:

 

You need to average your mileage over several tankfuls. It helps to stick to the same gas station and pump and let the tank go down all the way before filling it up. The auto cut-off at the pump can really vary depending on the station, temp, etc. There is also a thread about 10% ethanol gas that explains some of the possible mpg variance.

 

You can get a bad highway mpg if you run into headwinds (you said 55mph winds???), go significantly over 65mph, or have a loaded car.

 

I wouldn't worry too much if you just got one bad mpg reading. It happens.

 

Rule of thumb for gas mileage is three tanks of gas. the biggest cause for inconsisitancy in gas milage is your not filling the tank the same every time all the time. You need to use the same pump all the time and stop at the first click. Do not top off.

Things like tire pressure, snow on the road, a drginging brake caliper that happens only when the car is cold. A tank of very short trips as opposed to longer trips.

The other thing that is beyond your control is the weather. Barometric pressure, rain wind and air temp all have an affect. The temp of the fuel when it goes in the tank has an effect to. Cold fuel you will get more fule per gallon as opposed to warm fuel, which expands.

Have i given you a headache yet?

The best way to acheive optimal gas milegae for your individual vehical is to buy a vacum gauge. Try to keep the needle as high as possible and you will get the best milage you can in your car.

 

nipper

[WagonsOnly]

The low-octane gas available in Wyoming, plus the fact that no one actually lives there to use an entire tankerful in less than a year, may have something to do with it (at least that's my theory). For reasons I cannot explain, this past summer my VW's gas mileage dropped from ~31mpg mixed to around 28 hwy during the week or so I was in WY.

 

My guesses as to your mileage:

-Winds

-Bad gas

-Altitude (most of WY on I-80 is over 5,000 feet above sea level--Cheyenne is flat, but higher than Denver)

-Tire air pressure

-Gas cap--lost, missing, or bad seal

[idosubaru]

how the vehicle is driven makes a significant difference as well. and terrain (flat verses mountains).

 

driving to work, using the same gas station my mileage on my 89 Subaru XT6 is pegged at 25 mpg, doesn't vary more than 0.5 mpg. i drive 500 miles a week nearly all highway miles so i get very consistent conditions to compare, drive the same every day to work and back and mpg is almost always dead on.

 

take the impreza on roads trips and get the same thing, nearly 25 mpg almost exactly every time. within 1mpg. that one seems to sway a little more than the XT6, but still less than 1.0 difference each time. since my wheels/tires are larger than stock it's really over 25, but that's what the numbers come out to. (it's really whatever percentage difference my tires make, haven't calculated it yet, but probably only a few percent higher mileage). either way, the comparison is the same.

 

i'm driving 1000 miles or so this weekend in the impreza and expect the same consistent gas mileage, so i'd probably attribute it to driving conditions, weather, mountains or something like that.

[raulcruz01@earthlink.net]

Sounds to me like you might be leaking gas. Check your lines out, and aroudn the fuel tank.

 

I'm not smelling any gas. I did change the fuel filter recently, but lines look good.

[raulcruz01@earthlink.net]

The low-octane gas available in Wyoming, plus the fact that no one actually lives there to use an entire tankerful in less than a year, ...

 

I've heard there are 500,000 people in the entire state of wyoming It's BECAUSE of this fact we use so much gas because you have to drive a l-o-n-g way just to see another human being:lol:

 

Thanks for the replies. I DO think you're on to something re: altitude, octane, etc. I use 85 octane because somebody told me we don't have to use 87 due to the altitude. Is this right? Would you recommend bumping to at least 87?

 

I also pump cheap gas (at a minimart called "loaf and jug") or supermarket gas. I can't afford Shell gas, but we do have a Conoco. Would that gas be better?

[idosubaru]

i know nothing about gas. but i do know that years ago i did notice a couple mpg difference at the two local cheap gas stations compared to the others. a mile or 2 per gallon.

[friendly_jacek]

The low-octane gas available in Wyoming, plus the fact that no one actually lives there to use an entire tankerful in less than a year, ...

 

I've heard there are 500,000 people in the entire state of wyoming It's BECAUSE of this fact we use so much gas because you have to drive a l-o-n-g way just to see another human being:lol:

 

Thanks for the replies. I DO think you're on to something re: altitude, octane, etc. I use 85 octane because somebody told me we don't have to use 87 due to the altitude. Is this right? Would you recommend bumping to at least 87?

 

I also pump cheap gas (at a minimart called "loaf and jug") or supermarket gas. I can't afford Shell gas, but we do have a Conoco. Would that gas be better?

 

Here is your problem. I had nothing but problems with cheap gas: high sulfur, pinging, and unexplained low MPG. This is why I only buy from a major brand. However, I recently bought Sam's club gas (cheapest in town) and smelled sulfur in my Corolla, even though we are supposed to have low sulfur fuel since 2004.

Some no-brand outfits use the worst gas they can find on the market (possibly the washout batchs from the pipelines) and likely steal at the pump making you believe that MPG is poor.

If you want to experiment, buy gas only at exactly 5 gal amount. State inspectors use 5 gallons measuring devices and every pump is very accurate at this volume. Above that, your luck.

[tunered]

in my opinion there are big differences in gas quality,some even smell different,85 octane? i think 87 is the lowest around here.try a better known brand name,im betting it will help.remember you get what you pay for.[there are exceptions to this rule].

[nipper]

The low-octane gas available in Wyoming, plus the fact that no one actually lives there to use an entire tankerful in less than a year, may have something to do with it (at least that's my theory). .

 

 

You've got to be kidding. First off wyoming is a beutiful state and i would love to live there if i could find work. i am tired of living in a suburb of NYC. i have spent many miles out in WY, and the #1 reason for poor gas milage out there is the avg speed is about 90. i know in my sooby, once i cross the 72mph line, my mpg start to drop drastically. at 65 i used to get 32-34 in my 2.2 legacy, at 80 i would get 25, and 100 i would get about 18. Obviously you have never tried to go shopping for food in WY, where depending upon where you live, can take a tank of gas to get to the store and back. WHen i spent a fall out there (and fall is about 2 weeks, i was there from sept-dec) i was using 2-3 tanks a week due to where i was living at the time. i didnt complain because its a blast to drive out there where tripple digits are not unusual.

When i would ride out there on the bike from NY in the summer i would drop from 42mpg to 28 at 110 mph in wyoming.

The place where i would piss thourgh gas was indiana and nebraska, with really bad gas.

i havent had my outback on the highway since i bought it for any good long run, so i have no idea what that gets.

 

nipper

[nipper]

 

If you want to experiment, buy gas only at exactly 5 gal amount. State inspectors use 5 gallons measuring devices and every pump is very accurate at this volume. Above that, your luck.

 

Man this thread is full of alot of odd information

 

Where does your theory come from. The calibartion you have correct, as i used to do pump calibration. The inspecions are attempted to be done in warm weather to rule out fuel density issues since lab conditions are 68 degrees F when the pumps are tested at the manufacturer. the calibration is done three times to rule out human error. What they are testing is not so much the pump itself, as that gallon is fixed. What they are testing is the flow meterwhich actually reports the amounts of gallons pumped to the display that you read. The flowmeters when they were mechanical were tough to dicker with (you had to change gear ratios), so they were checking for wear. Now with the electronic flow meters, its real easy to play with the numbers and not pump a full gallon. This is where its important to know your car. You sort of know at 2/3 empty the car takes about x gallons.

it doesnt matter if one gallon or 1000 gallons is the sample size, its always the same test

The test can be started at gallon on the counter so therefore every gallon is the same. there is no diffenrce between startting at 26,007, 26,010, 26,015 gallons on the counter. it all comes out the same.

Acording to your theory, you are royally screwed if you get an oil drop of 250 gallons of home heating fuel, since its the same style pump, and the same people calibrate it.

 

nipper

[jman11]

Depending on how the mechanism works. Here's a simplified scheme, that would be found out, but you could make it work.

 

The machine starts off ignoring the 1st 1/2 gallon. So you get that for free. Then it counts every gallon as 1.1 gallons. The result would be that if you get under 5 gallons you gain a little. If you wanted 5 gallons you would get exactly 5 gallons. If you wanted 10 gallons you would only get 9.5. If you wanted 20 you would only get 18.5.

 

Whether this would make you money would depend on how much gas people buy on average; there are some doing better out of the whole deal (those who buy under 5 gallons), and some doing worse (those who buy more). It is still possible. If people buy on average under 5 gallons then you could reverse the whole process.

 

This could be made much more complex and harder to detect. It really depends on how the electronic counter works and how much power you have over its configuration.

 

If all you do is test a 5 gallon pour, then methods like this would easily show you as legal, whereas you aren't.

[raulcruz01@earthlink.net]

nipper,

I agree that Wyoming is an incredible state! i just came back from an hour of cross country skiing in absolutely beautiful country. It took me 15 minutes to drive to the trail, but couldn't go on the one I wanted because someone was sponsoring a x-country ski race. There aren't many places around that will allow the outdoorsman (or just the nature lover) to access nature so easily:)

 

I was talking to the guy I was skiing with about this "gas issue". He heard on NPR recently that pumping premium gas is a waste of money and that it was a "scam". I have heard that, at higher altitudes, 85 octane gas is just fine. Another TV show consumer scam show said that pumping 87 is pointless - that you should go one way or the other, but 2 more points in octane is negligible.

 

Anyways, this is interesting conversation. i will try a better quality gas station and see where that gets me.

[friendly_jacek]

nipper,

I agree that Wyoming is an incredible state! i just came back from an hour of cross country skiing in absolutely beautiful country. It took me 15 minutes to drive to the trail, but couldn't go on the one I wanted because someone was sponsoring a x-country ski race. There aren't many places around that will allow the outdoorsman (or just the nature lover) to access nature so easily:)

 

I was talking to the guy I was skiing with about this "gas issue". He heard on NPR recently that pumping premium gas is a waste of money and that it was a "scam". I have heard that, at higher altitudes, 85 octane gas is just fine. Another TV show consumer scam show said that pumping 87 is pointless - that you should go one way or the other, but 2 more points in octane is negligible.

 

Anyways, this is interesting conversation. i will try a better quality gas station and see where that gets me.

 

85 at high altitude is fine because of lower air pressue at high altitude. You still compress it the 10:1 or so but the net maximum pressure is going to be lower and thus lower need for antiknock property ("octane" number). Actually, lower octane has slightly more BTU value.

[daehttub2000]

Despite the savings (pennies) stay away from no-name or ultra-cheap gas stations. You get what you pay for. A friend of mine that owns a limo-taxi service forbids his drivers to use a number of the cheapest gas stations in Chicago. He learned the hard way. Fuel pumps, filters, mileage, etc.

[robm]

Fuel pumps these days measure mass flow, not volume, then correct it to volume at 15 deg. C. That way, you get the same summer and winter.

 

Rob.

[tunered]

where in the hell do you guys but 85 octane,i looked at 6 stations today and can find no less than 87 octane. they read 87-91-93 octane. i thought 87 was standard. reg

[nipper]

where in the hell do you guys but 85 octane,i looked at 6 stations today and can find no less than 87 octane. they read 87-91-93 octane. i thought 87 was standard. reg

 

Out in wyoming, Utah, Colorado Idaho Nevada to name a few.

http://www.summitdaily.com/article/20050812/NOTES/50812008

 

Oddly the article points out subarus specifically

Thats where the starter of the thread is from. 85 octane is still available in some states. At high elevation 85 octane is the same as 87. The country isnt flat you know.

 

nipper

[SQ93]

I tried to be helpful to area farmers by using the 89 octane ethanol, but it just killed my gas mileage by at least 10% and in some cases, more. My 1993 Legacy L wagon (236k) also did not run as well on the ethanol, particularly in colder weather. Warm weather (above 50 degrees F) and 87 regular gas and I get 22-24 city and 28-31 highway (even fully-loaded). Higher driving speeds and the gas mileage dips. Colder weather also makes it worse.

 

You will get odd mpg results on a single tank.

 

If you're really serious about getting a true mpg:

 

You need to average your mileage over several tankfuls. It helps to stick to the same gas station and pump and let the tank go down all the way before filling it up. The auto cut-off at the pump can really vary depending on the station, temp, etc. There is also a thread about 10% ethanol gas that explains some of the possible mpg variance.

 

You can get a bad highway mpg if you run into headwinds (you said 55mph winds???), go significantly over 65mph, or have a loaded car.

 

I wouldn't worry too much if you just got one bad mpg reading. It happens.

[raulcruz01@earthlink.net]

Thanks for the interesting article, nipper.

It's good to finally get some usable information re: octane ratings in gas. I'll stick to 85. Now the search for better gas at a reasonable price. One Shell station in town charges up to .14 more for their gas.

 

I've been doing some looking on the internet and I am closer to being convinced that I should start pumping better quality gas in our cars. So, in your opinion, which is better - exxon or shell? (these are the two higher quality gas companies we have in town)

[Andyjo]

i found that a new air filter (And a snorkle ) helped out my gas milage a bit. Even fully loaded (rear suspension riding pretty low) we were getting about.. 28mpg on the highway.. with the thule box on top. But now it's sucking again, so i'm gonna check my fuel filter, pull the sending unit and see if i can clean that up a bit.. maybe i'll grab some seafoam and slap it on the vacuum hoses... see what happens