Gas capacity and mileage questions

[e30cabrio]

We took our first trip this weekend to San Diego from Phoenix. Averaged 18.3 MPG @ an average of 75 MPH.

Filled the bit more than 1/4 tank in Yuma in an effort to avoid California gas prices. On the way back we pulled into Yuma with the needle on empty and the read out at 23 miles remaining and it took 23.90 gallons.



I thought it had a 24 gallon capacity.

My questions are is 18 on full freeway ok & did I really have .1 gallon left.

[TerminatorX5]

capacity is at 24.6 gallons - we just had this discussion on one of the unrelated threads just a couple of days ago... I somehow managed to fill up once to 24.058 gallons...

it is suggested that running on vapors is not a good idea, and I agree with it - it is just i am too lazy to fill up before i am below quarter tank...

i like your gas prices... a whole dime or two below what it is around this area... over 20 gallons of juice it is about $2-4... more money in your pocket, less money in BIG OIL pockets...

[sunny5280]

Originally Posted by e30cabrio

We took our first trip this weekend to San Diego from Phoenix. Averaged 18.3 MPG @ an average of 75 MPH.

Filled the bit more than 1/4 tank in Yuma in an effort to avoid California gas prices. On the way back we pulled into Yuma with the needle on empty and the read out at 23 miles remaining and it took 23.90 gallons.


I thought it had a 24 gallon capacity.

My questions are is 18 on full freeway ok & did I really have .1 gallon left.

18 MPG on the highway is about right for the 4.4i.

[e30cabrio]

I usually fill up at 1/4 the Ca border was about 40 miles back and gas was 4.559 there, 4.259 elsewhere so seeing as the car said I had the range I went for the savings.

My 94 80 series Land Cruiser is lucky to get 13 on the freeway from it's 4.5 6 cylinder. This is great mileage.

On a semi-related note, the read out says 14.9 right now after the trip when I got much more. I have reset it a few times do I need to do something else to get it to properly reflect the MPG?



Thanks

[motordavid]

Imo, the OBC mpg reading is a 'ballpark' at best...resetting it, moves the 'reading' to gather current driving situ, which can be drastically reduced by stop/go, city, et al.

If you reset it, leave it alone, and do a few tanks full of your usual driving: that will give you a readout that is in the zip code of what you are getting for that driving, during those few tanks full.

Doing the arith of miles driven divided by gallons over those same tanks full will give a more real world mpg, for those specific tanks full. The real number and the OBC may be close, or not.

Do the same, if curious, for day(s) long trips...
Your ~18 is about right; so is the <15 for whatever local condition your just drove.

The mpg readout is a telltale only, of recent driving conditions and gas use.

Fun to see it showing big numbers on trips, but it is often a bit optimistic, over time, esp on gentle cruise long trips, in my experience.

Add in the vagaries of fillups, (never the same pump, different temps and barometric pressures, never filled to the exact same fill point, etc.), and all one can do is record miles and gallons used to get a 'range', eg a 'mpg range' for 'highway trips' and a range for 'local/non-trip driving'.

After 12 yrs of our X, 11 yrs of our Vette, and other vehicles, I have a pretty good idea of what I should get mpg-wise on trips vs 'local'. None of it really matters other than anecdotally, and info for self...

Gas tank 'capacity': our '01 lists aprox 24.6 gals. We have come in on fumes a few times and taken 24.5, 24.4, etc. Again, dependent on pump, temp, bar press, and none of our tanks are all exactly 24.6, fwiw.
GL, mD

[sunny5280]

Originally Posted by motordavid

Doing the arith of miles driven divided by gallons over those same tanks full will give a more real world mpg, for those specific tanks full. The real number and the OBC may be close, or not.

I'm not sure I agree with this. This method of calculation assumes the amount of fuel you're adding to the tank is the same amount of fuel consumed. There's no way to be certain it is and, I suspect, it's not.

I spent a fair amount of time trying to get the computer to match the hand calculations. And I was never able to do so when calculating MPG between fill-ups. Over time the two came closer together. I suspect that's because the average eliminates the variances.

[tmv]

I average 19mpg in my 4.8iS on the drive back from Chicago when I bought it in June, 75-85 mph.

[e30cabrio]

On my 350Z the gauge was within a few mpg. This is 4 off which percent ally is huge.

Glad to know I had a gallon left.

[Qsilver7]

Also remember, as others have suggested, the fuel tank is 24.6...so there is a 99% probability that you had approx a bit more than 1/2 gallon of fuel left (0.7 gallons if we do the math). But depending on barometric pressure and other variables like how much fuel continued to flow into the tank just before the auto shut off etc...one can overfill the tank and fuel can rise up into the fill line...so more than 24.6 gallons of fuel can be put into the tank.

The OBC may not have the same avg mpg as your personal figures...again there are variables in play that we may not be accounting for. But there is a way to adjust the calculation if it is way off. If you've unlocked your OBC, you can adjust the calculation with TEST 20. You may not get your personal calculation & the OBC to be "exact"...but you can get them to be within tolerable proximity.

My suggestion is to track your mileage & gallons at the next few tank refills then average those numbers so that you have ONE "actual mileage" variable that you can plug into the correction factor equation...the correction factor equation (VK=correction factor) is: (Actual MPG / Displayed MPG) x 1000 = VK

[e30cabrio]

Thanks, yes I unlocked it to see voltage when my alternator went on hiatus. I would need to do 4 presses in test 20 if I find 18 is correct but I am showing 14?