Here is something that has bothered me for a couple of months now, it took me that long to notice the discrepancy, but I did not collect real numbers until now.

I bought gas Wednesday evening roughly six miles from home. I have a 80 mile commute to work, mainly on the freeway with little traffic except for the last six miles at night. At the 80 mile point I had 477 miles remaining at 31.6 mpg. I had Friday off and went nowhere at all either Friday or Saturday. Sunday is short hops from here to there to there to her. At the 85 mile point I had 460 miles remaining at 31.4 mpg. At the 90 mile point I had 436 miles remaining at 30.9 mpg. At the 95 mile point I had 407 miles remaining at 29.7 mpg.

Now here is what I can compute
80 mi + 477 left (557 total) @ 31.6 mpg implies a 17.6 gal tank.
85 mi + 460 left (545 total) @ 31.4 mpg implies a 17.4 gal tank.
90 mi + 436 left (526 total) @ 30.9 mpg implies a 17.0 gal tank.
95 mi + 407 left (502 total) @ 29.7 mpg implies a 16.9 gal tank.

The manual says I have a 16.2 gal tank.

The other little discrepancy is that I should have used 3.2 gal, about half-way between 7/8 and 3/4 full but the gas gauge shows a little over 7/8 full.

What can be trusted and when?

 

Well you have to keep in mind too that it's always going to be changing based on your MPG's, which would be changing constantly. If you average 35mpg, it's going to read higher miles left. If you are getting 28mpg while it still reads 35, it's going to be inaccurate until it goes down.

Don't cut it too close and plan on driving exactly those miles... I use mine as an estimate gauge.

 

Gas gages should only be used as a reference..they are not very accurate, and because of the shape of the tank and other electrical factors the actual amount will vary quite a bit at different gas levels,mine seems to drop the quickest after 1/2 tank when the shape of the tank starts getting smaller again...I have seen them at say 3/4 when parked then drop 1/8 at the next start-up.As far as milage..its still averaging out as you will notice a regular decrease as the miles go up until it settles down depending if your drive is the same for the entire tank...the DIC is ok for acuracy but milage versus gal used is the 'best' way.

 

mine is/was very acurate for a long time , i checked my milage on paper with a calculator. but recently i removed the fuzzy tube from my air cleaner, and have been flooring the gas pedal alot , because i like the new sound. now the dash thing is showing that i am getting better mpg. but it does not match my paper work.

 

1) Your typical analog Gas Gauges are not linear in response which is why at 1/2 tank reading you may have more or less. Every GM car I've had (based on manual calc )indicated 5/8, or slightly more on the gauge w/th approx half tank remaining. It cracks me up after a fillup on a road trip when I can go 100 miles and the gas gauge barely moves below full.

Unless you have instant MPG which is on 08?-09 models your DIC is showing average fuel economy(06 on up). Your miles left/economy is based is constantly being reaveraged from the moment you reset your fuel economy to the moment you read it.

 

They have instant economy on the new ones now? Dang...that'd be nice if someone were able to figure out a way to get that on the older models without! I'd love to have an instant reading, short of resetting the average econ every 5 seconds!

 

yeah you miles till empty is going to be calculated on your instant economy and you avg economy is well your average economy. this is prolly where your discrepancy is coming from. plus you have to calculate in the fuel that is in your filler neck when you fill up which could bring you closer to 17 gallons.

 

What's wrong?Wife ugly,can't get laid, JEEZ??Get a life,you actuality have time to figure out this Minor B.S. ? RANDY

 

Wow and they say I'm Grumpee

 

I've put 17.6 gal into the 16.2 gal tank - only once when I ran out of gas. I regularly put in more than the 16.2 gal. I'm still monitoring the gauge accuracy and the local gas pumps.