I can literally watch my gas gauge go down as I drive this car, have never had any other car where I can watch it go down lol.

I did some calculations and it just doesn't seem right. I bought the car in Modesto, and I live in Clovis, that is a 104 mile drive.

The car came with half a tank, and when I got home, it had under a quarter tank of gas. So, I would say in total, from that half of a tank, I would've got around 130-140 miles. That's 16.77 - 18.06 MPG.

The car is an M6, bone stock. No engine codes or anything, does this seem normal or is that bad?

 

for 100% bone stock that's not that great, but I don't think it's anything to be too concerned about. mine gets around 14mpg with nothing but lid, some POS flowmaster muffler the previous owner put on, and 4.10s in a 9".

however, when I drove it back from vegas after purchasing it, cruising at around 70 the whole way, I got something like 300 miles to the tank. with a combination of city and highway i get 200-210 miles to a tank. if i could manage 16-18 i'd be happy.

 

You should be getting around 20 in town 26+ on the highway

 

First, these gas gauges are not all that accurate.
Fill the tank completely full, reset the trip odometer and then drive it until whenever you want to fill up next (fill it all the way again). Then take those miles compared to how much gas you actually put in the tank.
Next, use 6th gear at any speed above ~45mph. These are toruqey engines, you don't have to rev to get up to speed, use that to your advantage.

 

I'd also recommend going back to the same station and filling up around the same time (hot vs cold temps can affect your fill amounts).
I drove 175 miles a day for seven years.
I got real good at comparing different gas stations.

I found I used more when filling up at the cheaper gas stations (Arco, AM/PM) (avg=14.5 gallons) than a station that charged 15 cents more per gallon (Shell/76) (avg=12.5 gallons).

If the car is new to you and you have been getting on the throttle a lot, that'll do it too. I noticed a considerable drop going from 3.23 to 3.73 gears. I can't blame it all on the gears. The response makes me get on it more

Lastly, I've read that changing out your rear O2s every 50K or so can help.
I've never done that, and have 150K+ on mine. I should change them out and see if it helps.

 

Forget the rear O2s, they only monitor cat efficiency. I (as well as many others) have deleted rear O2s on multiple LS1s, and there is zero change in driveability/power/MPG. It's the *front* O2s that will affect performance and MPG.

Good advice.

I will also add that there was unknown gas in the tank. Could have been old and/or too low of octane. So you can't put too much faith in those initial numbers.

 

After driving in an Accord for a couple years, took me a while to get used to driving my WS6. At first I always kept the revs up thinking I needed to downshift to get over minor hills. Only after reading that I didn't need to do that (I make more torque cruising than my accord made at WOT ) I kept my revs much lower and my mileage greatly improved.

Gas mileage is more of how you drive your car rather than what you have done to it

 

1. Your method of "calculating" your fuel mileage is absurd.
2. Air temperature is irrelevent when refueling.
3. Driving style has the largest impact on mileage, and this car is unfamiliar to you.

 

I beg to differ. Due to thermal expansion and contraction the density of the fuel increases when cooled and decreases when heated. Now granted, the storage tanks are underground and likely see little temperature swings but the fuel delivery system is not so deep under ground and is more susceptible to temperature swings. Its been said that its better to fuel in the morning at lower temperatures than later in the heat of the day.

 

Everyone who says that is wrong. I didn't quote anything else you said because it's irrelevant. Don't believe me? Record the fuel temperature in the coldest day of winter and again on the hottest day of summer. THEN come back a let me know if the temperature varies more than 15 degrees. The temperature differential required to see any relevant change in specific volume would be more than 5 times what you find.

 

Read this http://www.consumerwatchdog.org/reso...lUSAJune07.pdf I don't desire to match wits with you and get involved in a back and forth battle here I just thought your saying his "way of calculating fuel mileage was absurd" was a slam.

StryfeS13; As far as using the gas gauge to determine fuel usage it cannot be done in an F body car. Typically if the gauge reflects 1/2 a tank you are more than likely near a 3rd of a tank. The F Body tends to hang good in the greater than half a tank range and then drops like a rock at less than half a tank.

 

Use a little common sense!!!

Every 15° increase lowers volume by about 1% The MOST EXTREME temperature variation will result in less than 2% change in volume. That's less than a 0.5 MPG in the MOST EXTREME case. Real world observations would put this number at less than 0.1 MPG, thus irrelevant like I said. And claiming his calculations being absurd was accurate. Even YOU state you cannot judge fuel consumed by some vague markings on a fuel gauge.

 

Mythbusters did a check on gas volumes in temperature changes didn't they?

 

I agree; the calculation method was wrong and thus the results are erroneous and must be discarded.

As for the initial question, "Is this gas mileage normal?", no sound conclusion can be reached until the proper calculation method is used.

 

I'm a just a truck driver, but I shell out $80,000 dollars a year in fuel and do my own fuel taxes so trust me, I crunch numbers all the time. I agree with the others on here, you have to fill it up and then calculate the numbers. In fact, I'd take it a step further and say you have to fill it up several times and then average it out to come up with a credible number. When you fill it up, try to be consistent, like always fill up to the brim, or always fill it up to where it kicks off. That will help get you more accurate numbers.


As far as the temperature goes. This was discussed and researched in the trucking industry. If memory serves me right, the stations fuel pump's meter could be off as much as 5% under extreme temperature differences, thus resulting in a substantial lose of fuel when your talking 200-300 gallon capacities. However, once the fuel is in the vehicle (either with external return lines or closed within the tank) the fuel will quickly reach an average/normal temperature and thus not cause actual fluctuation in engines performance. I think there is a little truth to both sides of the argument, but in the end I'd say it probably wouldn't make a big enough difference on such a small tank in which the fuel was already there to begin with.

My car is a 2000 LS1, A4 with 115,000 miles, wearing all season tires at about 35-40psi. Earlier this summer, my son and I drove 4200 miles across the Rockies, up the California coast and then back home cruising 75-85mph with A/C on, did several burnouts, did a couple 1/4 mile test runs, got it up to 120+ a couple times so my son could experience that wind sound you get when you get up to those speeds, sat in rush hour traffic on the vegas strip, in LA, and in San Francisco, and we still average 24.29 mpg for the entire trip. So I think you need to re-check your numbers first and then if it's really that bad, then start trying to figure out what's wrong. Good luck.

 

Change both 02 sensors....they're probably factory originals.

.

 

I've been working as a valet for over 7 years, most newer cars display their mpg info (either in the odometer area or on one of the numerous information displays). Living in NYC where no one travels any appreciable distance on a highway, thus everyone is subjected to mostly "city driving", I can tell you that it has more to do with the driver than the car. I can park 10 honda civics with the same motor in one shift an they'll all have pretty good spread of gas mileage. When my wife drives our honda accord, she gets better mileage than I do, unless I'm trying to be efficient. While I'm not saying there aren't mechanical things that could effect your mileage, I think the driver/driving style will often dictate your mileage, the car's engine simply limits how good or bad you can make it

 

Okay guys. I filled the tank up from empty to topped off. I spent $61 dollars and got 15.1 gallons of fuel.

I traveled 302 miles on the 15.1 gallons.

So..20MPG?

 

Mixed driving? If so, that's about right. All or mostly highway should yield another 5-6mpg. Ideal conditions will flirt with 30.

You should monitor the mileage through the next few tanks to get a realistic average. That 20 could rise or drop a few.

 

consider yourself lucky... that same amount gets me 200 miles