marko3xl3

I really don't know what to think of this guys, help me make sense of it. Basically, the only thing that I did different on that tank of gas was drive about 1/2 of it on the highway, but it was a very hilly highway at high speeds. Usually those kinds of highways use up more gas, not to mention the stop and go on the highway. Is it possible that highway driving alone can bump up gas milage like that? My next tank (220 miles from now) will be Shell again and only my usual combo of city driving and we'll see what happens. But for some reason I have this itch...check it out:



P.S.: Some of those entries you see there include about 1/3 of highway driving (actually 55mph driving) and they still stay in the 14's.

I am really eager to follow this up, don't take anything for certain until I get to the root of this.

EDIT: I just remembered that on that same 16MPG tank, I replaced my front o2 sensor, but as you see the milage went down again soon after. Sucks that my new o2 sensor didn't make a continual difference. Does this affect anything?

Marko

Localmotion

Im guessing you are using the same octane rating for all of those. Also, you might want to try staying at a specific gallon IE 16 gallons filling up. I dont think the 8 Gallon Fill-up should be included in the results. The reason i say is b/c maybe you mixed 2 brand name fuels together which would skew the outcomes. The tank holds 18 and i think the 2 gallons you leave in the tank wont have a significant affect on the outcome.

98LimitedCustomized

If you attempt to only put in 16 gallons, what says it's full? However much goes in is what you've used, whatever the tripmeter says is how far you went. That 8 gallon one is fine....

You're due for trying Shell again, you're on track to potentially finding something but if you can't replicate it 3 times it was probably another factor.

Localmotion

well im just saying to use 16 as a constant number/independent variable to act as if the tank is full. If not, how are you deciding when to stop putting gas in? when it starts to pour out? or at the first auto shut off clicky thingy

98LimitedCustomized

Always stop filling once it automatically shuts of, never "topping it off"...

marko3xl3

It's always 87 ocatanes. Considering the o2 sensor is not a factor (else the milage should stay up longer) the only other thing I see is the fuel type and driving style during that fill up. Even if i mixed two gasolines together (which I did) and I got a better gas milage, it tells you something.

About the fill up thing...3rd gens are known for having a "safe" gas needle. When the light goes on you can only fit about 14.5 gallons in there which leaves about 3.8 gallons to go (about 50 miles). But I always take the safe route!

Localmotion

so start putting only 14 gallons in everytime. Then record the results. Maybe we are all looking too much into this..LOL

grimpy

Man I wish mine would light up at 14.5 ... When my light goes on, it only fills 13 gallons... I get under 200 miles each tank... I know I still have 5.5 gallons left but when that light comes on, I seem to automatically head for the gas station.

marko3xl3

Why does that matter, gas milage does not change because of how much you put into the tank. I always fill it up to full, and then I calculate the gas milage using how much gallons I used betweens fills and the change in odometer. The only important thing is that I fill it up top until the thing clicks the first time and not topping it off.

But even if I did top it off here is what would happen:

14G used w/ 200 miles driven = 14.29MPG
14.5G used w/ 200 miles driven = 13.79MPG

I do admit of being guilty of topping it off (about .50cents = .2 gallons), but that would REDUCE my numbers and not increase them.

marko3xl3

WOW, I thought I was bad. I would say you just drive until you get to 240, you should be fine. Other than that, it's really just an inconvinience. But I know how you feel, I get shakey too when the light has been on too long, just to find out I still had 2 gallons to go.

grimpy

I've been thinking about getting one of those gas containers filled up with about 2 gallons of gas, then take it to 250 to see how much I have left. With my avg mpg, I should still have 2 gallons left but damn... The thought of running out of gas blows!

I think I read somewhere once that if you run out of gas, you can get a citation for it in CA... I wonder if this is true.

Localmotion

I just think there are many variables that could be knocked down by having a specific amount of gas put in. I guess it doesnt matter unless you want to be more accurate. In that case, your method is/will work(ing) fine

marko3xl3

True, weight would be one, but that all decreases milage plus this would be going into huge detail and small numbers. I am definately going to pursue this more without making my truck a lab rat, because I have gained quite a lot there. As I said, I have an itch, but I think it's just a random occurence. We'll see soon.

Grimpy: It's not worth it. It's not good for your engine and you can calculate it yourself too. Again, it's only an inconvinience of 30-50 miles when you have to fill up. When you hit 250 miles I assume you'll have about 16.5 gallons used, another 2 to go . I also doubt officers give you tickets for going dry, it's silly. And yes, I really never wanna run out of gas either, it's embarrasing to say the least

midiwall

You also need to track the weather for the tankfull. San Jose is somewhat consistent, but temp and humidty can play a good sized roll in the mileage game.

X-AWDriver

My mom sees over 260 a tank in her '99 Limited and a fillup usually takes just over 15 gallons and with my Runner I get just over 230 a tank and I usually squeeze in not quite 15 gallons and the diff is the driving style between me and my mom's style since I used her truck for two weeks and I was able to bring her mileage down to match mine.
The funny thing is with a 5 speed on my '97 and with my driving style I was able to always see almost 270 a tank and now I really miss the 5 speed.

bamachem

you don't always fill up to the exact same level in the tank between fillups. you're probably w/in about 0.5 gallons every time.

now, if you're filling up w/ 14 gallons like you usually do, you have 14 +/- 0.5 gallons.

however, on only 8 gallons, it's 8 +/- 0.5 gallons.

as you can see, you have more room for error on the smaller fillup volumes. that may be the root of your high results.

repeat w/ shell for several tankfulls (minimum 14 gallons each time) several times in a row and then take an average of all 3 and that will give you more accurate results...

BTW, when I "top it off" I can fit about 1.5 to 2.0 extra gallons in there, so a 0.50 gallon error is very plausable and actually probable.

nrgetic99

Marko...

PM me for some off the record gas info...

David

tc

I work with analyzing data like this all the time and would be happy to analyze it for you, and determine if there is truly a difference between stations using ANOVA analysis. Gotta have more data though - at least 5 per brand. Get some more Shell data and post it. If you get enough data, the difference in highway/city driving will come out in the wash. Or, if you know what it is(was) reasonably accurately, I can factor it in using DOE analysis.

Some things I can think of:
Tire pressure vs weather - warmer weather = higher pressure = better mileage

Fill up the tank. It's the only way to get an accurate number. I go to the second shut off - there might be a lot of variation in the first shutoff due to the amount of air you are displacing in the tank IMHO.

Always use the same station (from a statistical point of view the same pump). There may be a difference in where the pump shutoffs are set.

ebelen1

Interesting stuff. First, you changed your 02 sensor and didn't see a drastic improvement in your mpg. That's good for me to hear since I was considering changing the 02 sensor b/c of mpg (no code).

I'm also very consistent w/ the numbers you're getting but I don't put the effort you do. I just divide the miles I've driven against how much the tank gets. It's always around 14-15 mpg. I know my speedo is off but based on calculators, the off-ness of the speedo doesn't make sense.

If I do what the speedo says (11% error due to increase in tire size), then I'm getting 16-17 mpg. I have a 3rd gen w/ full maintenance done recently. It has 95k miles. Good luck and def post results after a couple more fillups.

celica

I have noticed that on my toyota if I keep the tank almost full instead of letting it run down I get better mpg. This may be the case with that entry - something to look at anyways. It has happened over and over to me. At first I thought that I must be going crazy but it has happened on the Camry and the 4 runner. I can't come up with a good reason for it.